The precedents (in my mind) would be SP's with Cy Young stuff who were held back -- until age 30 -- by wildness and miscellaneous nicks and dings. And who then became strike-throwing machines.
Cliff Lee, if you count him, didn't jell until age 26, and then put up ten 200+ IP seasons.
Halladay battled mostly wildness, with a few nicks and dings, and then threw 2,700 IP.
Of course you have Randy Johnson.
Curt Schilling faced various problems until age 26 -- which limited his IP badly -- and then he threw 3,200 IP.
My general belief are that there are X number of bullets in a pitcher's arm, and if Paxton now figures out his 2+ BB form, he's as good a bet to have ten full seasons after that as anybody. Of course with Boras as his agent, they're not likely to be for us.