Since you posted this in the "Adoption" section, does that mean you are considering an adoption? A stepparent adoption by your current husband? I can't tell.
If you're just asking about a name change without an adoption, that's really beyond my scope. But I doubt there is any age cutoff. Even if he can't file it in his own name, you could file the necessary action on his behalf. But that would be a question for a different lawyer!