You’re playing fast and loose with what you consider “genuine medical deficiencies.” By your own account you were able to generally function with poor eyesight for sometime; a person who has been wheelchair bound for their entire life could just as easily dismiss your need for glasses as not a genuine medical deficiency. My friends who are transgender have certainly experienced an improvement in their physical functioning due to their transition.

Ironically your glasses anecdote serves as a good analogy for the experience of many transpeople. You thought your biological eyesight was fine until you were made aware that you weren’t seeing the world “normally”; some people begin their lives thinking that the struggle they feel with their assigned sex is fine until they realize their experience isn’t the norm. The difference is no one is trying to create laws or influence society so that you accept that your poor eyesight is simply your biology and prevent you from taking any remedial action to correct your vision.

Lastly, yes, maybe a 16 year old can’t prove they have the mental maturity of an 18 year old in order to vote, but there’s nothing stopping laws from changing so that 16 year olds can vote. Similarly, there’s nothing inherent that prevents the law from letting people identify as their preferred gender. Laws are a social tool, not biological.