Is it normal for fat to be distributed differently on one thigh than the other? 18 y/o

Could be: Although we have two of a lot of organs, symmetry is not a guarantee. Often one might have a breast larger then another, a limb shorter that another etc. So this could be a normal finding. It's also possible that this could be something more serious. I would have your doctor take a look, to make sure there isn't some underlying problem.

Sometimes: It's not uncommon to have some non-symmetric fat distribution (especially if you've had surgery or trauma to that area). But if there's a huge difference then it needs to be evaluated by a physician. Sometimes what you think is fat can actually be something else like swelling or an underlying mass (a cyst, lipoma, etc). There's no substitute for a good physical exam from a licensed physcian.