What are your thoughts on transgenderism?

I'm just watching someone say that to validate someone's belief that they are a different gender than what they were born as would be like validating a schizophrenics belief that they can jump off the Empire State Building and fly. Apparently transgenderism is defined as a mental illness and has been for a very long time. Is it a mental illness? I personally think that adults should be allowed to present and live as whatever they want. But when it comes to children I have very strong feelings against allowing them to transition. Kids aren't very good decision makers and I've seen too many stories about children regretting it later, which is so sad. Oh I'll attach the video in case you're curious. I only watched the first minute or two

[media=https://youtu.be/Xm4RaA17E4A]