I used to not drink and it wasn't until my third year at uni that I started drinking, which may seem a bit strange.
Anyway I never had any clear reasons as to why I didn't drink, but have sort of grown to assume the following reasons when I think back to it.
1) My family have never been big drinkers, my dad might occasionally have a pint if we were to go to a pub for lunch and they might drink a glass of wine if we were out for a meal but they never really drunk at home, maybe once or twice a month.
2) My brother had his own opinions of drinking and couldn't stand the idea of alcohol and has never drunk and I think I sort of looked up to him and so didn't want to either.
3) I was never with a group of friends at school who would drink from a young age regularly or go out and get drunk so didn't have the peer pressure and stuff for underage drinking.
4) Therefore when I became old enough to drink I never had so didn't know what to order if I did want a drink and didn't want to look stupid so found it easier just not to drink and stick to what I know.
5) Also I hated the idea of people getting out of their mind and absolutely wasted and couldn't understand anyone would choose to do that and decided if I ever did drink that I would do it in moderation and at meals, however I couldn't stand the smell of the wine or martini or beer that my parents drank and assumed it tasted like it smelt so I wouldn't like it.
I then kept this up all through my first two years at uni and hardly went out, though this was due to not getting on with my flat in first year, so not having people to go with, and living at home in second, making any drinking / going out difficult as I drove.
Finally lived out for my third year and was out at a social and it turned out the people I'd usually be with weren't out so I ended up drinking to make myself more comfortable in the situation. However for some reason I didn't start lightly, got myself heavily drunk that night so much that I have no memory of half the night or how I got home. You'd have thought that would have put me off but I actually felt so much more comfortable and less self concious as I used to feel if I went out that I have carried on, and probably now go out and get drunk once a week usually, though might also go to the pub with friends, and have found drinks that I like and like the taste of and am now one of these people I used to detest who go out with or without the aim to but end up wasted and I enjoy all of it, well apart from some of the stories I'm told after but as I can't remember it affects them more than me.