I keep my sobriety to myself, unless the other person brings it up. I also don't think it's a good idea to go into specific detail as to why I don't drink, especially early in dating. I just say "I don't like it".
Are you actually training for a triathlon, or did you just say that? Personally I would be careful about making something like that up, you never know when someone is going to view that as a violation of trust!
I think it is possible to date someone who drinks. After all, a "drinker" can be someone who only drinks a glass of champagne once a year on New Year's Eve. However, anyone who has anything remotely resembling a drinking problem, I will not touch with a ten-foot pole.