**Burning Wheel** requires using skills in a variety of situations in order to improve them.  Skills are mainly improved during play, but you can spend downtime for tests in skills.  Practice times vary wildly depending on the skill and the type of test (routine, difficult, challenging).  Burning Wheel Revised (the current, easily obtainable edition) does not have skill degradation; Burning Wheel Classic did, but it was removed to keep the bookkeeping simpler and probably because it wasn't interesting.

The lifepath system used in character creation means that your centuries-old Elf is significantly more skilled than a Man with the same number of lifepaths.  Without descending too much into the mechanics, an Elf could have grayed out his stats and have gray-shaded skills to match after character creation--a heroic edge over a Man's mundane black-shaded skills.  (Gray dice count a success on a 3-6 on a d6, whereas black dice only count 4-6.)