I personnaly plan on becomming a DM within my first year of diving, and instructor as soon after that as I can.
That said, do I feel I would be ready to teach a class on my own. NO. Do I plan to, no. I just want to get to that level, and then start helping other instructors I know, wether it be working as a DM (even though instructor certified) or helping with skill evaluations, etc.
I personnaly feel a person "could" be ready in that time, if over that 2 years they've been diving a LOT. (say 100dives a year for example, just a rough number) If they only did the bare minimum, probably not, but if they were out every time they could diving, they might be ready. Some people are natural instructors, and natural divers, with limited expereince they can demonstrate skills as if they have years of experience. (for example my buoyancy and air consumption are FAR ahead of the typical diver curve of a diver with the same number of dives as me, I've been told so by other divers and instructors as well)
I think even for the naturals they should get some expereience working with others though.
It is possible for him to be ready to teach and teach well. If I get my instructor cert as soon as I hope, the only people I might teach on my own would be friends/family, and no more than 2 people at a time most likely.
It would be interesting to see... it's possible for him to be ready to teach and teach well, but it's equally or more possible for him to not be ready to teach. Unfortunately theres no way to know for 100% certanty without watching him in action, going through a class, or sending someone through a class.
More likely than not, he isn't ready, esspecially if he's done most/all in warm water. Typically speaking thoose who are trained and certified (counting OW-Instructor) in cold water, are better divers (I've heard that from numerous sources) so I'd be even more leary if he did his certs in warm water, or though one of those internship things where they take an OW diver (or no diver at all) and make them an instructor in like 6months (in warm water)
Just my .02 cents... Probably not.