Hello, and welcome to The Student Room, great to have you aboard!
To begin, you are most certainly not too old: it's definitely possible to get in, and fitting in is more about being 'you'. I know for sure you will also get others who will do there best to be there for you.
It's great to hear that you're looking at a degree, and that's most certainly doable. As a personal experience, I knew someone who was ~40 and got a degree, so it's never too late. University's certainly a route to go, especially for Optometry which is quite a niche subject. In that case, a degree is probably your best bet.
I would always recommend checking out different universities and getting their prospectuses. That can give you an idea of the grade boundaries. You generally require Maths and a Science, but there's two ways around that if you need the science or if you need to up your Maths grade. The first is to retake your A-levels, and go from there - there are many online courses you can do that from. The second option is to begin with a degree in a science relating to optometry, but either as a Foundation Year, to begin a degree without the same requirements, or with the Open University. The Open University (if you haven't heard of it) is an online degree provider. It doesn't offer any specific courses for optometry, but you could take a science and from there get a Masters in Optometry with an in-person university. I'm not sure about Dispensing Opticians but in doing a science that still gives you the space to prioritise something else later.
I believe there are also Degree Apprenticeships in Optometry which might be worth checking out? An interesting alternative to both the aforementioned.
In the end, there are loads of ways you can get into it, so please don't feel that you're blocked from it all
. Everyone goes through these things differently, so you might discover something that surprises you. Best of luck with wherever you go! You got this