
If by dull you mean in his behaviour, coupled weith these bald patches I would ber thinking of having him checked for an underactive thyroid.
If it is this he will need medication for the rest of his life, but other than monitoring him, should be able to lead a fully active normal life.
my neighbour had 2 with this condition, one died at 12 1/2 last summer, and the other is still going at nearly 13!