At 60-ish, my age only bothers me when I think about how much I've missed by not transitioning before now and how much pain that has caused me. I mind some of the effects of aging -- I'm starting to get some arthritis in my hands and whatnot. But I would never want to go back to being 16 or 20 or whatever; I was miserable, knew nothing, and had no perspective about anything, and life is a lot more fun now that I pretty much know what's going on.
As far as looks go... I look at people who are 20 or so, and very few of them even have faces; they're just sort of blank, and they look pretty much alike. To me, the way someone's face shows their life is what makes them beautiful -- or not.
I did that test and my mental age came out to 35, which is sort of encouraging, I guess.