I wouldn't worry at all about starting a long course of study at age 23. However you're right to spend some time mulling this over, because medical school is a lot of work, and you'll not make it through the entire course on an initial flash of motivation.
Good to see another Uomo Universale.
I did physics, mathematics and more mathematics at A-level, only to go read law at university. I find it impossible to declare my exclusive allegiance to any particular area of study (well, er, let's rule out chemistry!). It's all good.
