I’m worried about loose thigh skin

With apologies to OP, since this thread is supposed to be about thigh loose skin and fat, not arm loose skin and fat: One of my li'l ol' lady cranky-rants has been triggered.

It's that "hangy upper arms" "when my upper arms are out to the side" thing.

When a person holds their arm horizontally and relaxed, there is a hangy, flappy bit. For most people, a fair fraction of this is not fat or loose skin, but rather relaxed triceps muscles.
(I'm not saying there is zero arm fat or loose skin, but will say that in every single case where this subject has come up in my real life, the person was at least partially identifying relaxed muscle as fat or loose skin. Women, in particular, seem to do this, even though men have it, too.)

Try this: Raise your arm so your upper arm is above shoulder level, bend tightly at the elbow (forearm toward upper arm), curl the wrist toward your forearm, and tighten up everything on your arm, especially the upper back part of the arm (triceps), flexing like a bodybuilder. Get it as tight as you can. Anything that firms up is muscle, not fat.

To make it clearer, when your arm is relaxed and horizontal, take your opposite hand, and grab the tissue of the upper arm, with your fingertips as close to the bone as you can get them, holding onto the "fat/loose skin". Then do the "flex like a bodybuilder" thing as described above. If it tightens up or firms up in your hand, it isn't fat, it's muscle.

Even quite-fit women, not to mention men, have triceps muscles that are mobile (will be slack, and "flap around" if the upper arm is shaken) when the arm is relaxed. This needs to be true, because muscles contract in order to do work, which implies that they need to have a little slack in them when relaxed. The longer muscles, like those triceps, will hang down with gravity, and move a little when held horizontally shaken while relaxed.