I was diagnosed with Hashimoto's at 22 and am now 39. Not sure what the most common symptoms are because I've struggled to keep my thyroid working so my symptoms are all over the place lol. Most common symptom for me though is hair loss, not going bald hair loss just falling out everywhere hair loss.
Most common found in the 40's but it is not unheard of to be Dx when in your 20's - 30's
Women are 5 times higher to be Dx - then men.
Hashimoto is auotimmune underactive thyroid. Many symptoms compare to hypothyroidism.