I agree that it's mostly fluff at this point, but that it certainly does (or could) matter in longer arcs and/or connecting between ancient heroes and the present (or vice versa), etc. At the same time, I really am not fond of the modifiers and approach taken in earlier editions either. I haven't had to use it yet, but my provisional plan for my own campaign:
There is, of course, a maximum age. Then radiating out from that are the "age bands" that are pretty familiar: mature, aged, elder, venerable (I don't worry about younger than mature). For each age band, beginning with mature, I impose one permanent level of exhaustion. So the mature figure simply isn't as spry as s/he used to be, and has a little disadvantage. By the time one is elderly, though, then those fights are much harder. Push yourself too hard when you are venerable (ie. gain any exhaustion), and your body might not be able to handle it.
Is it perfect? No. But it's simple to just add the exhaustion modifiers to both PC and NPC characters, and it lets me use the stat block for NPCs (or PCs) from their halcyon days of youth with minimal effort. I also like to stock previous campaigns' characters as NPCs in current campaigns. So I can take a PCs old character sheet when their character was in their prime, and just use it unaltered but with permanent exhaustion levels to represent them in the new campaign (depending on how much time has passed between campaigns).
There is, of course, a maximum age. Then radiating out from that are the "age bands" that are pretty familiar: mature, aged, elder, venerable (I don't worry about younger than mature). For each age band, beginning with mature, I impose one permanent level of exhaustion. So the mature figure simply isn't as spry as s/he used to be, and has a little disadvantage. By the time one is elderly, though, then those fights are much harder. Push yourself too hard when you are venerable (ie. gain any exhaustion), and your body might not be able to handle it.
Is it perfect? No. But it's simple to just add the exhaustion modifiers to both PC and NPC characters, and it lets me use the stat block for NPCs (or PCs) from their halcyon days of youth with minimal effort. I also like to stock previous campaigns' characters as NPCs in current campaigns. So I can take a PCs old character sheet when their character was in their prime, and just use it unaltered but with permanent exhaustion levels to represent them in the new campaign (depending on how much time has passed between campaigns).