Not travelling more as a young and unencumbered woman. I never made it out of Europe really. Now this seems like a pipe dream!
Not being brave enough to actually have sex before I was 24! I wasn't short of interest... I still don't know why I was so screwed up about it.
Not being brave enough to have a relationship with another woman. I know that's part of my make-up but I was too chicken to take the leap when I had options.
Taking the career route I did. Should maybe have done a vocational MA and ended up in a sector I might have enjoyed. As it was, I allowed myself to be flattered into an academic MA and then PhD and ended up in academia (briefly) which I hated. I have no career now (partly because of caring responsibilities, see below).
Having my children later in life. I was 34 and 37. Now I'm 50 and so tired.
Deciding to have a second child, actually. Although I wouldn't have made that decision to have an only child back when I was fertile ... our second child has severe autism and LDs and - well, I wouldn't wish him away, he's loved and lovely (mostly). But our lives are now always going to be different. As we get older, he'll need to be living somewhere residential and that terrifies me: the potential for abuse, unhappiness, GUILT. But we're knackered in our early 50's! And my first child will, eventually, be saddled with the responsibility of making choices for him. I find this very hard to cope with and it's a constant source of anxiety and depression. So yes, sometimes I do wish I had somehow known, and made the decision not to have a second child. 