I was diagnosed in 1995 with PA aged 43. I passed my PADI Open Water qualification in Israel in 1997 and Advanced Open Water in 1998.
I confess that living in Britain, I only dive in warm waters on holiday. I see no reason why an averagely fit PA person who is receiving appropriate treatment should not dive, though I think they should take gentle dives in good conditions initially, accompanied by well-qualified and experienced leaders.
I think my air consumption may be higher than it would otherwise be, but that is the only relevant factor. In a group of divers there are usually others who get to 30 bar before me!