I am 42 and I have been dealing with this for the last few years. It comes and goes but when it comes it's hard to get any work done. My best advice is to stop working when the pain starts, sit in a proper office chair the right way straight up do not slouch, take frequent breaks, do RSI warmup stretches, and finally get a personal trainer to get the blood flowing in the arms. I do all of these things and even have switched keyboard layouts. I current use whisper c++ to dictate my slack convos and work emails. As for the mouse use I have tennis elbow from mousing I have not figured out a way yet to stop that, I'm going to try mouseing with my left hand and see if that is doable.
Not everything is at scale. We have adopted these techniques (at the beginning of this year) for our internal web frontend to our build system at work and it makes it possible for all of the team to work on this system without having to setup a complex node environment or deal with npm. We also get the pretty shiny that Tailwind brings to the table. Our system is as simple as can be but not any simpler.