Yeah, I'm in the same boat age wise. And I've found it is now quite scary how fast I can lose my skills, and how long it takes to come back.
You're more experienced than I am but this age stuff is a whole new world of issues.
Note that I practice fairly active lead for about 2hrs EACH DAY at a minimum, plus optional rhythm and combo lead rhythm when I have time and energy.
And my fingers and hands just manage to handle it ok. There are limits that if crossed, can injure my hands. You don't want that !
In case some of my advice might give you a different perspective, I'll list the following :
1) First thing of the day is to gently stretch as many muscles in your hands you get to. Then, do up to an hour of slow focused warmup, take a break for half an hour, then...play your heart out with your fingers and brain warmed up and ready... for an hour to start with...with the goal of two hours or so. Believe it or not, having your fingers pre-warmed up before practice makes the brain/body connection so much more satisfying.
2) Try not to use your left hand for much, except guitar ; let it recover and store up energy for the next day.
3) Play EVERY DAY, even if it's only for 20 minutes. This is key.
4) Always play to a beat of some kind...even in the warmup. I use a metronome in my warmup daily.
5) At our age you will have tired days and sick days and allergy days etc. On those days just do what you can but don't skip a day unless things are really, really bad. Life interruptions will force a day off once in a while and that's all you want.
6) Once your hands/back/arms are in shape, consider splitting your practice into two sessions. I've found this tends to supercharge my average tech capability considerably. It is a little bit more of a strain on the hands so use carefully. But a double practice seems to be better than one long one in my experience. It's a little too hard on my hands so I don't do it often. I use a lot of fast picking, finger vibrato and slides though. Your stuff is likely simpler and a double practice might work brilliantly for you.
7) Try not to let your callouses get wet or damaged. If they do get soft and moist somehow, dry them before playing. I sometimes use a hair dryer !
8) Design your practice so that there is focused work on weaknesses but also allocate part of your practice on simple pure FUN too. I find this really helps to motivate me through long slogs of "work" practice. Gotta have a FUN time ! Experiment with FX, different chords, different beats, different songs, record goofy sounds...whatever you think is the most fun. I like playing lead along with whatever comes on the radio. Or fiddling with a looper.
9) And you might consider icing your left hand after each workout if you find your hands extremely inflamed/stiff. I have these freezing wrist wraps from the dollar store that probably aren't a buck anymore or even available. A bag of half frozen peas is my backup.
10) And no one likes this advice, but try and keep the rest of your body in the best shape you can get it. Having hands that are in Olympic form without a fit body to support them is...limiting. So exercise a bit more. And watch out for inflammatory foods and foods that weaken you. And big meals prior to practice. And of course, get a lot of good sleep. Sleep, or lack of it, is a major factor in performance, trust me.
Of course you probably know all this, and the rest of the chop-regaining process, but our bodies have changed over time and new limiting physical and mental issues abound. I wouldn't have needed most of these steps when young...but the game has changed, right ? Sure has for me !
You've got 5 months to get in top form and maybe you can get there they way you are doing it, but I'm a bit doubtful you can afford to take any days off.
I suppose it's possible if the music is relatively low tech. But to have precision feel and expression, that takes time and work of course.
Hope this helps and hope you make it the way you want !
It sure ain't getting any easier...
