Yeah, the generalised judgement here makes me uncomfortable.
I am autistic, ADHD, and hypermobile amongst other health issues. Unfortunately, the truth is that for many of these are simply comorbid conditions; they don't tend to come alone. As people here know, there is a huge overlap between being autistic and identifying as trans, but equally there is an emerging overlap between being autistic and having EDS, autoimmune conditions, hypermobility and other related conditions. Naturally, you are therefore more likely to see young people who fit into these groups using canes and other mobility aids than young people outside of them.
I have a few friends who are simultaneously autistic, trans, and use mobility aids to help with invisible disabilities. Equally, I have non-trans autistic friends who are similarly disabled, and autistic friends who aren't disabled. Some have brightly-coloured hair, some wear "wacky" fashion, some don't. Some use mobility aids all the time, others intermittently. Some wear sunflower lanyards, others don't. I've had to use a cane myself to combat chronic pain in the past, and thankfully I haven't had to recently. If I do have another flare-up I imagine many people would look at me the same way; they have before. I know I'm not faking my disabilities, and I know my friends aren't faking theirs either, but none of us are carrying round doctor's notes to prove it to anyone who fancies a question. Some of my disabled friends refuse to use aids at all to avoid the judgement.
The truth is that nobody can tell from sight alone whether or not someone's disability is "legitimate," but in all honesty you shouldn't be trying to guess that at all. This kind of judgement, as demonstrated by disabled people on this thread, only serves to hurt all disabled people. We already face enough judgement and doubt, especially with the recent discussions around PIP.
It's not your business. Leave it to people's doctors.