Bkidd: it is never "too late" to neuter, but the greatest benefits for the dog come if it is done early - before puberty. In the case of a cryptorchid dog (one or no testicles descended) it is best that they be neutered as soon as possible as retained testicles have a high chance of turning cancerous. Before 6 months is best, and preferably before 1 year. But any time is better than no time
The demodex makes things rather more difficult in your case. How bad is the mange and how is it being treated? I'd be looking into trying to boost his immune system as much as you possibly can and when you get the mange under control, get him neutered as quickly as possible.
Incidentally, yes cryptorchidism has a genetic inheritance. It is thought to be a sex-limited autosomal recessive trait - meaning that the dog must inherit two copies of the responsible gene (one from each parent) but that only male dogs can actually be affected (obviously LOL). Kat: that means that
both Cassius' parents had to be carriers.
That makes it a difficult condition to screen out of a breed - because those dogs that have only one copy of the gene (carriers) won't be visually identified and bitches never will be even if they have two copies of the gene. Obviously, a male dog with an undescended testicle(s) is easy to identify and should never be bred from. Because of the high risk of an undescended testicle turning cancerous, neutering as soon as possible is wise - but once that is done, there are no further health implications for the dog.