I bought my first Spandex-y garments last year at 33 when I re-took up running, and now I run around my town three or four times a week in short, Spandex shorts and feel totally fine about it. I realized that I never particularly pay attention to what any other exercisers I see are wearing (unless it’s something that looks really cool), so there’s no reason to think that they’re doing that to me.

Edited to add: also going to a gym where older ladies are always hanging out fully in the nude as they change into or out of their swimsuits has been helpful in this regard. I figure if they’ve decided there’s no point in spending time worrying about other people seeing them naked, I should follow their example and not waste my time either.