I'd say...stay 18! hehehe.....anyway, I'd tell myself to take care of myself better and only do what I'm comfortable with. I'd mention to NEVER do assembly line work, or take crap from people (even if they're friends) and never be too dependent on others for happiness. Never get into credit card dept. ....I'm sure there's more to tell myself, if I think about it, but, it's better if I just take it from here and not make the same stupid mistakes.