I recently posted a query to other players, trying to see if anyone had any ideas about slowing or preventing the usefulness of external macro programs in UO. Reece replied and suggested aging. This is an idea I had heard before as a role-playing and realism suggestion, but the bonus of reducing macroing made me decide to pursue it.
You specify an age for your character when you create it. The younger you start, the harder it is to gain skills but the longer your character can live. You can start at any age, and below a certain point (say, 15 years), your character is represented by the child sprite. Below another point (say, 30 years), you cannot choose grey hair or beard. This will help identify players' ages by appearance, which should benefit roleplaying and realism. As characters age, the appearance can reflect that: some characters may end up with receding hairlines, grey hair, longer beards, etc.! Wigs and scissors should be allowed to "fix" this, along with hair dye.
As a character ages beyond physical peak (25 years), it gets harder and harder to advance stats. Eventually, stats (not skills) start to decline irreversibly. Very late in life, skills start to get hit as well; before this point, the character should consider retirement or a quest to regain his youth (see below).
At any time beyond, say, age 30, a character can opt to retire and "have a child" who inherits a large amount of the skill set (but not stats) of the retiring character. The child can start at any age up to, say, 15 years younger than the character (so if the character retires at 35, the child can be up to 20 years old).
As an alternative to retirement for determined characters, there are quests that will restore a character's youth. These are extremely challenging and not necessarily particularly rewarding in terms of years of life restored, but allow a character to continue on without losing stats and skills. Perhaps a visit to each shrine without the use of any magical transportation (Teleport, Recall, Gate, or moongates) is sufficiently difficult that not everyone opts for the quest, and some characters do retire (the goal).
You age at a constant rate for each minute you play the game, it's as simple as that. So you age from talking, from fighting, from macroing, whatever. With UO time being approximately 12 days per real day (I believe), each year would last about a month; this is probably not fast enough to have any interesting effects, so UO characters should age faster than we might expect from real life experience. One way of accomplishing this and also encouraging sensible play would be to have players age faster when they die or get injured. An expression we hear in real life (after a particularly tough game of tackle football, for example) is, "that took a year off my life!" In UO, it would really happen: taking a lot of damage (or dying) would add to your age.