I find measuring youth by nights out an odd concept.
Being young was about freedom for me, and nights out were a very, very small corner of that. At 22 I was living in my own in Japan and spending my holidays from work exploring Japan and Taiwan with old school and uni friends who came out to visit, or on my own, or with new friends. It was a life I couldn't have lived with a husband and baby in tow. I could choose to go anywhere I wanted. I moved all over the world, always working and relying on myself, before I married at 30 and had my first baby.
A lot of travel opportunities are really very much more easily available to the young. Youth prices tend to apply up to around 27 or 28, working holiday schemes used to be available up to age 30 but I think some have expanded to 35, suggesting "youth" stretches perilously close to chronological middle age!
Having a spouse and baby bars you from a lot of the perks and opportunities of youth, so it stops you falling into that category I guess. If you just never wanted to do those things then it's no skin off your nose! I did want to do those things, so to me early 20s is still young, because it's a time when the world's your oyster if you aren't tied down with responsibilities.
Vodka really has nothing to do with it, plenty of people whose children are grown up go on nights out!