I got my PPL for my 40th birthday, one of those life milestone things, go and do something you always wanted to, realise an ambition.
I suspect it's not your age that's the problem. You've already alluded to it in your post: by now I am also used to making decisions, taking responsibility and being in charge of large teams. Even on management or technical training courses that I attend, there is respect from the other attendees for who I am and what I do, and I am far from being a complete novice. How long is it since we were complete novices at anything?
Compare this with learning to fly. It is very difficult to sit in an aircraft for the first time, thinking you know quite a bit about aviation (it's been a hobby for so long), and then realise you can't even steer the thing on the ground. The instructor will be some baby-faced, just out of nappies pre-teen with thousands of flying hours, who may be a little impatient that this old fart (he's used to training bright-as-a-button 17 year olds) seems to take weeks to get the hang of the basics, will he ever get far enough to fly by himself? And how does it reflect on him that you're taking ages? At this age I sometimes felt embarrassed at how long it took me to master these basic skills, and as for remembering all the information, well... truly back to being a novice, for the first time in years.
But that's also part of the attraction, it's a challenge, and let me tell you that the rewards are worth it. Keep going. Do it for yourself, don't worry about what that spotty oik in the right hand seat thinks of you as a person (and anyway, he probably doesn't think any of the things you are feeling: you're most likely not as slow to learn as you think, you're just so used to picking up things quickly). In the end, you'll be able to fly off on your own, into the clear blue yonder, leaving all those earth-bound cares behind. Fantastic. I still feel SO privileged to be one of the ranks of aviators, that I (another ordinary Joe) am allowed to do this, which very few of your colleagues can. It is indeed worth every penny and every hour and every cringe-making cockup.
Stick with it, you are not alone.
TAFO