I'm heading towards the big 4-0 myself and can definitely relate. The thing is though, you can't live with regrets. The choices you made were the choices of who you were then, and like it or not, that person is still a part of you today. The path you chose may seem like it was the wrong one, but you may never have discovered the things you love, the people you love without having dealt with all the crap that you now look back on and hate.

But, just my opinion, as I'm going through some similar stuff.
*hugs*
happy birthday.

Don't worry about looking back, look forward, if your job has you pinned, change jobs, at least start shopping, if you don't look, you'll never know. Pushing yourself and growing your skills is important, it seems you know that already.

Yay happy belated birthday.