I see nothing wrong with preferring a night in over "going out" just for the sake of not seeming old.
Hell I'm 33 and I'd rather stay in most nights.
LOL, just a few weeks ago I was having dinner at a friend's house, and after a little smoking she got a little silly and had an urge to make some coffee. While making it, she turns to me and says "Look, it's 10:30 on a Saturday night and we're making coffee. We're old."