Take it from an 'old one' here...divorced, did some bad things in life, etc...we tend to beat ourselves up for what we did, but I heard some good sayings while I was trying to get over my past...they are as follows..
"There are no mistakes in life, only lessons". Very true...we learn often more from tough lessons than the easy ones!
"Cryin over a bad past is a good waste of tears"...so true.
Everyone has things they regret...and you know what? People that judge you for your lessons/things you did, I have seen that that is often a reflection or a mirror of something they did or were affected by...remember, its their crap and try not to take it on if this is affecting you.
Also, my counselor told me, "how would you feel if your best friend said all the mean things to you and your mistakes you are saying to yourself?" Then why would you do that to yourself?
We are never too old for a fresh start...and those of you in your twenties...trust me on this...you are definitely not too old! You have so much of your life ahead of you! We are never too old; so remember that please, and be nice to yourselves...
Hope this helps...Im better at giving advice than minding my own!