In my own background, I had a fairly intense playing schedule while I was in the Coast Guard Band, but for 23-1/2 years after that I worked full time at a non-music job. Between the demands of the job, and the time it took me to get this site up and keep it going, there was not as much bandwidth available for practice as I would have liked. (My discipline is not the best, so I probably could have done a better job at carving out more practice time.)
During this later time I honed my skills at multi-task practicing, where I try to practice 2 or 3 skills at the same time. Some of the videos I have on YouTube talk about this. Mostly, I need(ed) to be sure to NOT waste the time I had with the horn on my face.
If there was not time for a good session, I would try to warm up at least. Just make good sounds and cover as much range as practical. The longer sessions were spent in various ways. Sometimes I would focus more on some skills than others, depending on what I wanted to improve. There were a few recitals along the way where I worked much harder and more consistently for 3 months or so, but that pace was not sustainable all the time.
THIS NEXT PART may pertain to Dennis and others, and was also of benefit to me.
For a few years in there I had almost no practice time. However, I found it possible to still listen to music while commuting, in the background while working, and other times. I found I began to appreciate music more deeply. Perhaps there was room in my attentions to really absorb the beauty of music when I did not spend so much time with a "music/work" mentality. While in the band, every time I'd hear a neat solo piece or orchestra piece I'd find myself analyzing how it might work for euphonium or band. I still do that, but it is more balanced now. Anyway, during that time I believe my musicianship improved! I had built more "stuff" inside me to draw on while playing.
I suppose it is like our normal sense of taking a vacation. We do so to refresh, and in theory come back to our everyday life with new energies.
There are obviously physical considerations with aging. We heal more slowly, and some of our bad playing habits affect us more. For a few months now I have focused on relaxing my chops more while I play (that has been a weakness of mine forever). My joints are not as healthy as they were 30 years ago, so I have to work more on getting finger dexterity where I want it. And the simple fact is I may not be able to play as fast as I once could.
So far my ultimate range has not suffered - it has actually improved on both ends. But my building my endurance takes a bit more attention.
In summary, compared to 30 years ago, I'm not quite the technician I was, but I'm a better musician IMO.