User blog comment:Almiralovestwilight/What if JACOB is turned into a vampire?/@comment-4747248-20120707140252

"I buried my face in my hands and shuddered at the thought, at the very real

possibility. It could have happened so easily. And werewolves didn’t react to

vampire venom the same way humans did, they’d told me only now. It was poison

to them." -

It is mentioned here that Shape-shifters can't turn into vampires and if Jacob wants he can continue phasing so his age would not increase.