Man...I was as wild as they come from 20-30...it was a way of life. Up all night, sleep all day. I really never stopped and thought about it at the time. I DO remember making fun of the old men in the club that were around 40...

Your metabolism usually slows down around 25...this is when you normally start gaining weight if you're not active or don't work out...you also start to look noticeably older than the predominant, younger crowd...
Going into your later 20s, it's not as easy to crash on a couch or floor anymore after partying...because you know you're gonna be sore and feel like shit...the older you get from there, the worse you feel the next day...
It's really different for every person though...depends on how long and how hard you've been doing it...or if you even CARE to want to slow down and/or find someone special....for some people, partying helps them stay "young"...some people party hard for a few years and get it out of their system...then look to settle down.
I'm thinking YOU should go with your gut...you'll know when enough is enough. You're way more mature than most guys your age...maybe you're ALREADY slowing down on purpose....due to your subconscious...
When I was a teenager, my personal plan was to live life and get to know myself and what I want in my 20s...and then settle down in my 30s...and that's exactly what I did...
I wasted alot of time and money....which was stupid...but it worked out alright for me...I don't have any regrets...but I shoulda got my shit together earlier...say at 25. I'm 36 now.
Sorry for the long post...but this is a serious point in a man's life...when to start putting away the childish things and becoming a responsible citizen...I wanted to share and help if I could...