Let's consider a hypothetical. I want to run a campaign that takes place over a long period of time, which means that characters age quite a bit as the campaign progresses. A human might start the campaign in their 20's and end in their 60's, and that's not nothing. How can we make age relevant both narratively and mechanically in D&D 5e without stooping to the use of d20/Pathfinder's ability score adjustments? What I'm thinking is to define four age categories: youth (children and teens), adulthood (20's to 40's), middle age (40's to 60's), and old age (60's or older). Narratively, you don't need to do anything in the rules to make those age categories meaningful. For example, NPC's are less likely to pay attention to the opinions of someone in their youth or old age, those in their adulthood but not quite middle aged are more likely to find a mate, and so on. Also, it makes sense that the DM might give advantage to an older character on a History check or advantage to a younger character on a Charisma-based check, depending on the situation. Mechanically, there should be something interesting that makes the player feel the effects of old age on their character without being boring, fiddly, or (most importantly) un-fun. In d20/Pathfinder, there are permanent ability score adjustments as characters age. Basically, STR/CON/DEX goes down while INT/WIS/CHA goes up. I don't think that's interesting. It doesn't make players feel the effects of old age on their character; it makes players feel the effect of penalties. And penalties aren't fun. I think each age category other than adulthood should have one or two rules that are easy to describe and easy to follow at the table that make each age category feel different without just making them feel penalized. For example, things like advantage/disadvantage on particular kinds of rolls, levels of exhaustion, modifications to short and long rest recovery, and so on. Brainstorming, I think I like the idea that a middle aged or old aged character gains one level of exhaustion after each combat encounter. That means that during combat they still get to play and have fun, but after combat there's a consequence to deal with. For a middle aged character, they can recover 1 level of exhaustion after each short or long rest, but for an old aged character they can only recover 1 level after each long rest. On the other hand, an old aged character might have advantage on all Wisdom saving throws (making them an asset when they are in combat before they get exhausted), and a middle aged or older character might have advantage on Intelligence saving throws (which are not terribly common but make characters an asset in certain encounters when they are past their prime). That's just one idea. The goal is to avoid decreasing anybody's fun while they're playing the game while also making the effects of age apparent... and while letting the normal leveling and feats system encapsulate the rest of their growth and development. What are some ideas you can think of?