Dexterity issues will happen to all as we get older, but it is the story behind them that is the answer to minimalising there effect on us.
First off, injuries we sustained when younger may become more apparant as we get older.
As our bodies age we do not repair as fast, injuries take longer to heal.
Also if we had an injury when younger our body may continue to heal it throughout our life...until we slow down, then the rate of healing is not as fast as the damage, so it become apparant to us...usually a an ache.
For me having a daily routine to repeat that covers all range of body movement give all my musicles and joints a chance of movement that they may never get in actual day to day life.
So my warm up when i wake up is all about stretching and a varied range of stretching.
Because i use the same routine, if something is not right i can feel it, if movement is restricted or sore i can feel it. This is like a "bench mark" for me it makes me aware of wat is going on.
My playing warm up is the same, it is playing scales and execises in the same way as usual so as to inform meall is well......or if something is wrong. Only by having the same routine can i assess this, using varied or changing routines serves me no purpose.
Because my warm up has vast arrays of movement, i give my hands, wrists, forearms, elbows, and shoulders a full chance of movement, again movement i may not get when in a playing situation.
When working i may have the same score, or songs to play night after night, so my movements will develop a routine, a routine of movement that may favour some movement, but not others. So my warm up gives me a full range of movements or which only some may reflect what i am about to play......but it does not neglect what my body can do in favour of what i play.
This along with better diet, staying better hydrated, less longer practice times in favour of short ones with lots more breaks helps me stay where i need to be, rather than where i want to be.
Accepting change as we get older is not a lose of skills, more over a different way of using what we have.
I suffered the worse thing of all, a sudden and complte lose of function through a car crash in which i broke my neck. The immediate effect was paralysis on the right upper body, and weakness to the left side resulting in complete loss of all movement in the right arm.
That was 7 years ago and although i have my skills back they are greatly depleted in the "headroom" i have when playing. before the accident i used less than 50% of my skills to play 100%, (100% is to play mistake free, 50% is the effort used to do so) so in playing terms i had 50% in the tank if i needed it.
So if un-well, tired or run-down i could still give 100% but using maybe 75% effort.
In practice, or rehearsal, learning material was faster or slower depending on the amount of effort i had to use was another example of headroom, some days learning required just listening and no playing, so learning songs was just learning arrangments, not physical playing.
In the end we have to use what we have, not what we had, and that requires a change of attitude more than anything.....My grandfather once told me "when you are young you can work from the neck down, but in later life at some point it pays to start working from the neck up."