I'm not sure what kinds of actions you're referring to since much of what teens do is immature and can be foolish. My opinion of people isn't affected much by knowing what they may have done as a teen, even professionals, since I know people often change dramatically from their teen to adult years. If it was something criminal or otherwise alarming, that might be different, however.

That said, I would not want my T to share much about themselves. I've never had a T share so much personal info that I've lost faith in them and I am glad for that. A T using their own behavior to "normalize" things isn't good therapy, in my opinion, since that assumes that because a T did something that makes it the norm, which it absolutely doesn't. It can absolutely change how a client sees them if it exposes very different set of values.