I don't think it's an age issue...I'm 50 myself and fit and have good legs, so I'll go mid-thigh, even at work. Personally, I don't care for short boots and skirts together....for me, I wear short boots with pants and tall boots with skirts, whatever the length. Also skirts with regular shoes...whether heels or clogs or whatever, that's fine. Something just rubs me the wrong way about short boots + skirt.
I think you can wear whichever length skirt you're comfortable with. Before I clicked on the link, i thought you might be talking about knee high boots, which I like with a skirt that skims the top of the boot on 'mature' women ;-)
I really like that length of boot (and openness of the top of it) with knee length dresses, or just below the knee (those are pretty much the length of dresses i have). Above floor length and longer than knee (like tea length) can make a gap of leg showing that is a little choppy looking, in my opinion, but i could be wrong.
Some links i found through google.
Edit to add, most are saying that knee high boots should be worn w skirts that show a few inches or it looks dowdy. Good point! I was wrong!
Dammit!! Now I want to go shopping!!