Back in the early 1990s, BA Flight Engineers were no longer necessary with fleet upgrades etc.
A number ended up at BAe Prestwick to train for the CPL/IR under CAP509. Various ground school credits due to their FEng qualifications.
Age band 28-44.
The youngest had no problems, whilst the oldest wisely gave up the unequal struggle at the end of the SE phase.
It was certainty the case that on the whole they did learn slower and found it harder than the usual BA cadet in their early twenties. That I doubt would come as any surprise: “old dog and new tricks”
I see no difficulty those in their 30’s starting to train. Modular route is probably best, with the PPL course a good point to assess whether continuing on the route is worthwhile. An experience instructor is best placed to access your potential.
Those with a low golf handicap aged 40 - 45 will more than likely be successful as well. Demonstrating good hand to eye coordination and a sound temperament when playing those difficult shots out the rough or bunker.
Once you pass aged 50, on balance, the odds are not in your favour. Stick with PPL flying and enjoy it. Choose your days carefully.