Elderly dog doesn’t understand his limitations

So, I have a 17 year old Schnauzer/Beagle mix. We've always gone on 'adventures' together frequently, which are really just walks and hikes in lots of different parks and trails. Exploring has always been his thing much more than play, so I use a harness and retractable leash and just let him do his thing. He's definitely slowed down in terms of speed and stamina, but he doesn't seem to know it. He still starts out at a fast trot and will wear himself out after 15 minutes or so. A couple of years ago, I bought a dog stroller so we could still take long walks together, but I could put him in to rest when he got tired. The problem is, he'll only rest for like three minutes before he starts fussing to get out and walk again. Even when he's in there, he's standing up half the time. It's not that the stroller really bothers him; he seems to appreciate it when he's really tired, he just has FOMO I guess. He gets so wiped out after these walks and I can tell he's a bit sore after as well. Any ideas on helping him to accept that he needs to kick back and enjoy the ride? I'd love to keep him out longer on our outings in the fresh air and he loves to socialize with people and other dogs, but I really don't want him overdoing it at his age.