Not surprisingly, Wendy is of two minds about getting older. First, unlike Peter, she recognizes that getting older is just a natural element of the human condition and every person must face it, with the exception of the lost boys. She also feels a greater sense of inherent responsibility than Peter does, even when they are both children. That is one reason that Peter wants Wendy to come with him to Neverland; in order to care for him and the lost boys. When she first meets Peter, she asks his age and his reply surprises her. He says,

“I don't know,” he replied uneasily, “but I am quite young.” He really knew nothing about it, he had merely suspicions, but he said at a venture, “Wendy, I ran away the day I was born…

“It was because I heard father and mother,” he explained in a low voice, “talking about what I was to be when I became a man.” He was extraordinarily agitated now. “I don't want ever to be a man,” he said with passion. “I want always to be a little boy and to have fun. So I ran away to Kensington Gardens and lived a long long time among the fairies.”

Wendy is enchanted by Peter’s explanation, not so much by his desire for eternal youth but because he knew the fairies. Later, when they pretend that the children are their children, Wendy accepts the so-called responsibility of caring for them and even of aging. She goes to Peter “and put her hand on his shoulder.” Wendy then asks,

“Dear Peter,” she said, “with such a large family, of course, I have now passed my best, but you don't want to [ex]change me, do you?”

“No, Wendy.”

…

“I was just thinking,” he said, a little scared. “It is only make-believe, isn't it, that I am their father?”

...

“You see,” he continued apologetically, “it would make me seem so old to be their real father.”

Wendy accepts the responsibly that comes with getting older. She also realizes that there are many joys as well. For instance, “years rolled on again, and Wendy had a daughter.” Wendy apparently loves her daughter and tells her stories about Peter Pan. When the girl, Jane, asks Wendy why she can't fly, Jane answers,

“Because I am grown up, dearest. When people grow up they forget the way.”

“Why do they forget the way?”

“Because they are no longer gay and innocent and heartless. It is only the gay and innocent and heartless who can fly.”

Even if she feels somewhat wistful about growing older, Wendy takes great joy in being a mother, sharing her stories with her daughter and reminiscing about the days when she was young and carefree and could “fly.” When Jane flies off with Peter, Wendy sighs but allows Jane to go.

J. M. Barrie presents Wendy Darling as a sharp contrast to Peter Pan. She is a sensible girl who understands that, before too long, she will join the adult world that her parents inhabit. While Wendy enjoys being a young girl, she has outgrown the absorbing early-childhood period. As the oldest in the family and the only girl, Wendy is often responsible for her younger brothers, such as stepping up to help her parents find Michael’s missing medicine. She is very close to her mother, who provides an excellent role model so Wendy has no qualms about what the future entails. Sometimes Wendy and her brother play at being their parents, with Wendy imagining the happiness of becoming a mother.

From the very beginning of the book, the topic of growing up is stressed. Wendy is shown to have learned about the temporary quality of childhood when she was just two, as her mother expressed her regret that her daughter would not always be such a delightful toddler: “'Oh, why can't you remain like this for ever!'”

By the time Peter enters the story, Wendy has begun to see that her childhood might not be lasting much longer. Her dreams of Neverland and Peter focus on a boy who does not grow up. When her mother looks into her children’s mind while they sleep, she is surprised to find Peter there, as she had heard of him when she was young. Wendy, when asked, denies that Peter is grown up. Not being grown up and his stature are key elements of his character, which Wendy takes pain to demonstrate as being like hers.

“Oh no, he isn't grown up," Wendy assured her confidently, "and he is just my size."

When Peter comes and they converse at length, Wendy is initially quite wary about the idea of flying off with him, although tempted by the mention of fairies and mermaids. It is his appeal to her maternal side that wins her over. While Wendy wants to have an adventure, she is also drawn by the domesticity of the arrangement he suggests—to tuck them in at night, and darn their pockets.

How could she resist. "Of course it's awfully fascinating!" she cried.

At first, Wendy might not want to grow up, but she accepts the inevitably of it from an early age, unlike Peter. We know this because the narrator tells us:

All children, except one, grow up. They soon know that they will grow up, and the way Wendy knew was this. One day when she was two years old she was playing in a garden, and she plucked another flower and ran with it to her mother. I suppose she must have looked rather delightful, for Mrs Darling put her hand to her heart and cried, "Oh, why can’t you remain like this forever!" This was all that passed between them on the subject, but henceforth Wendy knew that she must grow up.

Nevertheless, Wendy is pleased to go on the adventure to Neverland with Peter. However, she accepts and embraces the idea of returning home and becoming an adult. When she comes home, she goes back to Neverland every year for a time to tidy the place up but never stays. Eventually, she grows apart from Peter.

Wendy becomes the symbol, at least for a time, of the woman who cares for and protects the boys who don't want to give up being boys. The story shows that boys depend on someone more mature like Wendy to keep their lives carefree. The narrator tells us that Wendy is, in the end, pleased to assume an adult role:

But the years came and went without bringing the careless boy; and when they met again Wendy was a married woman, and Peter was no more to her than a little dust in the box in which she had kept her toys. Wendy was grown up. You need not be sorry for her. She was one of the kind that likes to grow up. In the end she grew up of her own free will a day quicker than other girls.

Wendy is the oldest Darling child and although she clings to magical ideas like playing with mermaids, she also cherishes the idea of being a woman and a mother.

In chapter 6, when Wendy awakens and Peter introduces her to the Lost Boys, they tell her that they have built a house for her and beg for her to fill a void:

Then all went on their knees, and holding out their arms cried, “O Wendy lady, be our mother.”

“Ought I?” Wendy said, all shining. “Of course it's frightfully fascinating, but you see I am only a little girl. I have no real experience.”

“That doesn't matter,” said Peter, as if he were the only person present who knew all about it, though he was really the one who knew least. “What we need is just a nice motherly person.”

“Oh dear!” Wendy said, “you see, I feel that is exactly what I am.”

Immediately, Wendy falls into this maternal role, rounding up her "naughty children." She spends many joyful nights with the boys, tucking them in at night and sharing great stories with them. This maternal role is one Wendy feels destined for and growing into it even younger than anticipated doesn't trouble her.

In chapter 17, years pass between Peter's infrequent visits to Wendy, and eventually he returns to find her a married woman. She is no longer the wishful girl who adventured with him:

Peter was no more to her than a little dust in the box in which she had kept her toys. Wendy was grown up. You need not be sorry for her. She was one of the kind that likes to grow up. In the end she grew up of her own free will a day quicker than other girls.

Wendy simply matured out of childish fantasies earlier than many other girls, and even though she promises Peter that she will never grow up, she accepts the changes that growing older will bring. Still, she relishes the magic of Peter and his magic so much that when he returns after she's become a mother, she allows her daughter, Jane, to fly away with him and be his next mother for a while.