Welcome to the forum and to Glider Parenthood.
If he is 3 years old and intact - you would definitely see a bald spot on his head and a yellow stained patch in the middle of his chest where there is another prominent scent gland.
If he has been neutered and it was "pom off" it might be difficult to tell the gender without separating the fur some on the belly to look for a pouch.
If he had a pom on neuter, there will be a small fur covered "pom" in the middle of his belly.
Since he is new to you, it is always a good idea to have a glider seen by a glider experienced vet
for a well check up and fecal testing to make sure he is healthy and has no parasite issues that might require treatment.
At the same time, the vet
can verify the gender and do a nail trimming during the visit.