1. Speed. I can't play uptempo tunes (250+ bpm) without the tune getting ahead of my brain. Result - more mistakes, erratic tempos.
2. Stamina = fatigued after about 30-40 minutes of solid playing.
3. Arthritis (knees/hips) - affects mostly bass pedal play; able to play pedal-only bass only on slow and medium slow tunes.
4. Memory - remembering changes from familiar but infrequently played tunes.
5. Complacency (aka laziness
) - lack of desire and incentive to learn new tunes (I don't think I know any tunes from this decade).
I'm sure there are more subtle things but these are the ones that stand out for me. How about you?
Good topic, As far as the those what I consider extrema up tempos, just slow it down and gradually bump it up. Stay relaxed and breath!
Stamina - take breaks and stretch.
Memory- keep a note book. I've slowly been converting my decades worth of charts on my ipad, using On Song app. No shame in pulling out your notes. Hey, even Sinatra used a teleprompter later in his career for songs he had been singing over 50 years.
Complacency- try to get together with other musicians, and I'm sure they'll call tunes that are new to you. It also great to have accountability partners, even if you just have to prepare for a rehearsal band. Also consider studying with a teacher. Classical, jazz or whatever you're into or want to learn more about.
Go to performances, check the greats and up and coming musicians on you YouTube, and try to keep an open mind. You can find plenty of motivation even in styles outside of your comfort areas.
Of course make sure you eat healthy, exercise, rest, and I also believe meditation is very beneficial for musicians.
As musicians, we are life long learners, and that in itself is a good thing for all of us as we age.