Quote Originally Posted by Thrice Dead Cat View Post
Make them minor things. I mean, in the purpose of combat, a year may seem like a long time, but it doesn't matter much if the guy you're stealing said year from is going to die the next round... that or lives another ~500+ years +/-1d100.

Maybe have it be based off of Spellthief and sacrificing things like sneak attack for other benefits?
The spellthief-esque idea is great! And the stolen years are more for the timethief's benefit (gaining more time to work with, considering the prices are going to be quite steep) than an actual detriment to the target, though I'd imagine a time thief of a high enough level could actually age a half-elf or halfling (to say nothing of an orc or human) to death.