The encounter with the older women at the Lavender Bar is one of many situations in the book in which Holden 'fails' to connect with adults.
Holden wants to feel he belongs to the adult world and do adult things eg. go to the bar and drink alcohol.He is knowledgeable about it too: he knows, unlike the women, that Tom Collinses are not a drink for the middle of December. However, he is simply not old enough and the waiter refuses to serve him. Knowing about and being interested in things is not the same as being able or ready to do them.
Having failed to get a drink he then immediately pursues more adult behaviour which is beyond him: he attempts 'chatting up' the women who are at a nearby table. Holden has already estimated them to be in their thirties which makes them nearly double his age. When they understandably giggle at his adolescent advances they are denounced as 'three real morons'. Holden is very critical but one could have predicted such a reaction.
More negative comments about the women follow: he criticises one of them for speaking in a way he considers affected. He dislikes for example, the way she refers to the toilet as 'the little girls' room'; no doubt this is an artificial way of speaking for a woman in her 30's. However, one of Holden's opening lines to the women is 'Would any of you girls care to dance?' which is a similarly affected way for an adolescent to talk. He could have recognised that he shares the same tendency and been a bit more tolerant.
To sum up, this incident shows: firstly, Holden does not yet 'belong' to the adult world; secondly, if he is to receive love from others, he must accept their faults as ones he shares.