I have a yellow female betta with cataracts. I’ve never seen or heard of this before, so I was wondering if anyone else had. Any causes besides old age?

To the best of my knowledge, cataracts are caused by mild fungus on their eyes.
You could try treating her with anti-fungus. I know they do make one specifically for the eyes - I think it's called something like Fung-Ex or something close to that.

There is also a condition out there called cloudy eye. One of my WalMart boys had it horribly. Unfortunatley he didn't make it past a few days cuz he had ick and who knows what ever else he had. Cloudy eye can be caused by lots of things - infections is the most common cause.

I'd probably try upping the water changes and seeing if that helps at all - if it gets worse, I'd consider treating with something anti-fungal or anti-bacterial.

Good luck!