No he's not too young - these are scent glands, which, working as they should, should never need manually emptying. With the passing of a normal stool they should release a small amount of the fluid. They are never meant to be empty. If there are periods of abnormal stools - looseness or diarrhoea, they can become overfull and clog up, perhaps becoming infected. And this is what's irritating to a dog.
Do NOT allow a groomer to do the manual draining - a vet needs to do this to see what comes out and whether it needs treating with antibiotics.
As far as I'm aware, anal gland problems have nothing to do with genes other than just maybe as with one of my hounds, they are situated too far in for me to be able to drain myself. My vets have problems doing this too. I suppose that could be down to genetics as he's a big hound - everything is BIG. The only connection that I know of with diet, is not allergies, but rather if the diet isn't producing normal stools - in which case even if drained and treated, they will refill and the situation will happen again until the diet is corrected.
Worms is another possibility and would cause itching.