You did the old boy proud. Labs can be delicate with age with joints and their stomachs are sensitive.
I'm facing the decline of my black lab. He's 13 this year and he's slowing down rapidly. Still a happy old boy, but he can't handle a lot anymore. We did Snowdon on Saturday and that damn near killed him. Last year we did pretty much every mountain worth bothering with and he was fine. This year he's struggling. He's now officially retired but it's going to be weird not taking him on big adventures. Have a slightly younger cocker and some ratdog crossbreed also. Still, been very lucky with him, no real ailments to complain about and an amazing dog everybody loves. When I was younger we had one go to 18 and one to 15. Exceptional luck with our labs.
Sorry for your loss, it's the way it goes and you can just be proud that you gave him the best life possible. Mine are always rescues from mistreated circumstances so are always special to me simply because of the work gone in to make them a viable pet. I'll never be without a dog. Don't let it put you off in the future. there's plenty out there that need and deserve owners such as yourself.