I'm "too old" to go back at 6. Well, I'm not old-old, but I'm 43, and the idea of reliving through the entire childhood and adolescence is simply too much to bear.
Doing basically all of school again.... then high school... trying hard how to remembering how and when I made some friends and redo on purpouse some crucial steps that happened casually... it's simply too much.
Some of my biggest passions are music and traveling, and I did both a lot, so it's not that if I go back, I would see so many more concerts or have many more trips. I'd only want to have a chance to warn close relatives of cancer appearance, but then again, how would I do it? how would I time it? I'd have to relive through nearly 30 years to maybe drop "casually" a month too late, and out of the blue, a "hey uncle, how about you get a brain scan"?
So no, there are things I would gladly chance in my life, but not at the cost of reliving years and years to get through them, and and at the high risk of butterfly-effecting my life into something I don't remember or want anymore. Give me the money.