As has been mentioned, E6 pretty much does this. Yes, it's 3.5 edition, but there is little need to port it to 4th as it's merely a concept that can be used for any edition. It's simple. Freeze level progression at a point you like. However much XP it took to hit that last level is how much it'll take to get an extra feat. So in 3.5 it may have required 5000 XP to go from level 5 to level 6, at which point the character is maxed out for levels. So after that point, another 5000 XP would gain a new feat, and another 5000 XP after that would gain another feat, and so on. In E6, you can gain pretty much every feat in the game if you play long enough. In my game, I cap it at 20 extra feats. I also run it up to level 14 before imposing the "no more levels" rule.
You can add some extras if needed -- for example, e6 relies upon the idea that there are feats in the game that will extend a class in appropriate ways. A wizard will take a feat to gain an extra spell. A fighter will raise his BAB or HP. 4th edition might need some logical extra feats if the splatbooks haven't extended the feat selection enough yet.
Also, again for 3rd edition but easily extended to 4th, there are many optional rules about stuff taking time. From the DMG there is a training rule that leveling up requires a number of weeks of practice with someone of your class and of a higher level. From the PHB 2 there is a rule that retraining and rebuilding options for a character can take a number of weeks as well. Finally from one of the complete books, there are teamwork bonuses that can reqire weeks to gain (but are otherwise free of cost). I impose many of these restrictions in my game. They aren't boring, as the players can fast-forward through the time -- "Hey DM, we all train for 3 weeks in town, OK? Thanks." However the net effect is that years go by before they hit level 20. Keep your towns spaced out and require travel for quests (as in LotR) with only a few wandering monster encounters per journey, and you will indeed have the "seasoned veterans who saw many battles over many years." You don't even have to endure a lot of complicated math and rules changes. What I've described is fairly easy.