Our lab Cooper is 13 and slowing down - how do you handle watching it happen

Cooper has been with us since he was 8 weeks old and he'll be 14 in July if we're lucky. for the past several months he's been slowing down in ways that are hard to watch. takes longer to get up from his bed in the morning. sometimes pauses on the stairs like he's deciding whether it's worth it. doesn't sprint to the door when i get home the way he used to - he still comes, he just walks now.

the vet says he's healthy for his age, no obvious pain, labs came back good. but "healthy for his age" is doing a lot of work in that sentence, you know? he's still Cooper - still wants belly rubs, still loses his mind over cheese, still comes and puts his head on my knee when i'm working. but something has shifted and i don't know what to do with the feeling it gives me.

i'm not posting because anything is wrong exactly. i think i just wanted to talk to people who understand what this phase is like. how do you make the most of this time without turning every day into a goodbye? and practically - is there anything i can do to help him feel better or move easier? i don't want to be passive about this.