You missed the point.
Nick's gotten old, and he's not getting any younger. As one gets older, one becomes more prone and/or susceptible to injury. There's wear and tear, a certain degree of deterioration. Even something as simple as a deep bone bruise can prove more problematic when you're "old." Blah blah blah.
But that doesn't make any sense. Being in one's 40s--especially when you're in world-class shape like Nick is--does not increase susceptibility to a bone bruise, nor will being of that age--again, especially when you're in such great shape is Nick is--affect the degree to which it heals.