Okay, I'm on the verge of creating a new persona, but I don't see any maximum age to be accepted into a Crafthold? Is there one?
I think any age can be an apprentice. I know children have to be at least 12
I don't think there is one officially, but they don't have as many late starters unless you maybe count dragonless people going back to learn a trade. There was mention of that in the books a few times like Lytol weaving. But as far as taking them, it would be up to the hallmaster I'd think.