i have been bitten many a time by my female veiled.. it doesn't hurt as bad as you would think.. just shocks you for a moment..
my male ambanja got me once as well.. and he is never aggressive.. ever.. but i had latex gloves on because i had been cleaning out my roach enclosure and i think that maybe he didn't recognize me.. he drew blood.. it wasn't the most pleasant experience, but still.. not horrible
it seems like my veileds starteing getting more aggresive about 3-4 months.. maybe a little later but not much.. i think it coincides with sexual maturity.. i also have two male panthers.. neither of which are aggresive at all, so i suppose species has something to do with it
Mine only tries to bite if I'm holding him. I got my first bite when he was about 5 months old.
He won't attack if I just put my hand in to clean the cage, etc. But if I pick him up to move him somewhere, and carelessly happen to get my fingers in front of his gaping (hissing) mouth, he will clamp down. And yes, it can hurt. The last time left quite a neat V-shaped cut in my finger.
Moral of the story is: don't get your fingers where they can bite. Give them space to move, and they won't feel the need to bite.