I am a 45 year old guy who has a 23 year old irlfriend
That's not a big difference in the scheme of things, not something you should worry about (you should maybe even count your blessings)...
Although I am 45 I take care of myself and workout 3+ days a week
This is important for both your sakes. Not that 45 is old.
and no gray hair (thanks to my genetics).
Genetics or no genetics, grey hair can be turned to whatever colour you like with a can of Grecian mousse and 30 seconds in the bathroom :-)
and our lve for each other grows stronger day by day
That's good. Nearly all relationships have their crisis eventually and you should be prepared that in yours, when that crisis happens, age may well play its part.
I could be old and healthy or I could be wearing a diaper and have t be taken care of.....
I know couples with similar or larger age gaps than yours in both those situations and they manage, even when age-related illness comes into the picture. I think from the fact that you write 'gray' 'college educated' and 'diaper' that we're from different countries, however by the time you're older, you'll probably have a normal National Health Service or something close to one and they are very used to providing support to people and their younger (or even older) partners. Remember, all it takes is a car crash or a serious illness and it could be you who is pushing the wheelchair rather than your partner. Unfortunately, I speak whereof I know. That doesn't diminish your love though.