I have a 7-year-old girl. I noticed a little gray above her eye like a year ago; it was very subtle....then, everything snowballed! She's got cataracts now, and she no longer looks (or moves) like a puppy. She limps when she gets up and walks.
But...She still plays with my giant-breed puppy, so that's heartwarming.
OP, I think your pup will stay youthful-feeling because of your other dogs.