I agree with Sharky- always, when in doubt go to the vet. Even if it seems like nothing at all- it is better to catch it as soon as you notice
That being said, I will tell you that my orange girl, Chichi, is 17 years old and has developed "age" spots on her lips/gums, and eyes. It is caused by the sun
but go ahead and take him in to rule out any skin cancers or other skin problems
Do you have any pics of it?