Does hypothyroidism/low thyroid cause premature ageing?
No, it doesn’t cause premature aging. Hypothyroidism can cause myxodema which is characteristic skin changes, especially on the face and hands, where you skin has a thickened, coarse dry or puffy appearance. It can also cause hair thinning, and a yellow tinge to the skin in severe hypothyroidism (from high plasma carotene). These symptoms however will go away once you’ve started treatment and your skin will go back to normal. As you don’t appear to have these symptoms yet and presumably have started thyroxine replacement then I wouldn’t imagine you’d get them as your thyroid levels should be improving.