Atticus is described as old and feeble at the beginning of Chapter 10.
Scout never gives any specific physical descriptions of Atticus. The closest you will come is the quotes at the beginning of Chapter 10, when Scout complains about her father’s age.
Atticus was feeble: he was nearly fifty. When Jem and I asked him why he was so old, he said he got started late, which we felt reflected upon his abilities and manliness. He was much older than the parents of our school contemporaries… (Ch. 10, p. 116)
She is concerned because his job is not exciting. He works in an office! Where is the romance in that? Being a lawyer or legislator does not float Scout’s boat. She is too young to realize that what her father does is important. She would rather he operate a dump truck.
More importantly, he looks old.
Besides that, he wore glasses. He was nearly blind in his left eye, and said left eyes were the tribal curse of the Finches. Whenever he wanted to see something well, he turned his head and looked from his right eye. (Ch. 10, p. 116)
All he does is read. He doesn’t have any vices, like drinking, gambling, or smoking. This man is as boring as they come. Scout will not find out until later that he is actually quite interesting, when the mad dog threatens the neighborhood and she learns that her father is a dead shot even with one good eye.
When Scout is disappointed about her father's age and general appearance, she is looking at him from an immature perspective. She has no idea how important her father really is to Maycomb. During the trial, she will learn that he is the town’s social conscience. You don't need perfect eyesight for that.
Note: Book editions will vary, but these page numbers should get you close enough to find the page in your book.