I would strongly argue that diving only two weeks per year is very dangerous. It's about the worst thing a diver can do. There is no way to maintain skills with such infrequent diving. PADI even recommends taking a "refresher class" if it has been 1/2 year sinse your last dive. If you want to limit the risk, limit the depth but he'd be much better off diving every couple of weeks year round then only twice a year. At the twice a year rate he will remain a "novice" forever.
Airplane pilots have a requirement to fly so many takeoffs and landing within a given period or they must fly with an instructor again. I'd like to see this become the norm in diving too. Maybe a rule that you need to be supervised by a profesional if you have not done 6 dives in the last 6 months or something along those lines.
But in 6 months even followign PADI's minimalist guidelinds you's be due for a refresher class.