I am sorry that you have concerns for Gus Pippa, I understand as I am in the same position as you as my Jasper is now 13 years and is beginning to show his age.
I see that Gus has a good heart, whereas Jasper has a Grade 6 so the heart is his concern, as far as I can see Jasper has no joint problems and when out is very mobile, he does sleep a lot and sleeps very sound which we have mentioned to the vet who says it`s just part of getting old.
The hot weather we have had recently really knocked Jasper about, which made him cough more and was panting quite a bit, both dogs had a vet visit last week so we brought up our concerns about Jasper, he said that if he started to lose weight, did`nt want to walk or started to have fits to bring him back up straight away, which we would anyway, he still eats well, like his walks, so the coughing was the issue, we now have to split his water tablet to twice a day. The vet said Jasper is now on the tipping point so he could introduce further medication, he has been on the same meds for the last 3 years.
I also grew up with dogs, they all were about 13 years old when we lost them, so this plays on my mind as well. We all want our pets to have the best possible life and it`s hard to see them growing old and it is the not knowing what to expect which I find hard as Jasper is our first family dog and like you we have had him from a 8 week old pup.
Hope all goes well at the vets on Monday and let us know how you get on.
and my two special boys Jasper age 13 and Ollie age 3.