If you were to time travel into your younger body but retain your current memories, what is the youngest that you could go and make it work to your advantage without just going insane? Late 20s, early 20s, late teens, early teens or even younger? The further back you went the more you'd be able to play the future and (somehow) buy Microsoft shares in the 80s etc but Alanything less than about 18 (late 90s) I think I'd snap.