“Age is just a number” was probably coined by someone unrealistically ambitious. In the literal sense, age is, in fact, just a number. However, our biology is not impervious to the laws of the universe. The ticking clock that is life has claimed many ambitions, and a lot of the times, we can do little but surrender to its whims.
While age is just a number, it is also the reason why you can’t become a world-class athlete, an MMA fighter, or a professional swimmer in your middle age. However, some pursuits in life don’t abide by the tyrannical impulses of time, and, luckily, becoming a doctor is one of these exceptions.