Dark Jezter said:
They can be housetrained, but it takes time. If they go on the rug, just rub their nose in it until they learn.
Which takes about 80 years. The best way to house train them is to put them in the woods. That way, they're in the normal environment, and if they do go--you just rake it over with a little dirt.
Seriously though, elves are not stupid. It's just that their culture is different. Elves not reaching adulthood till 100, is like human's not reaching adulthood until 18/21. A thousand years ago (in europe), or 300 years ago (in the America's), children were considered adulthood at puberty. A 15 year old boy/man was considered responsible enough to start a family, go to war, etc. His girl/woman was probably only 13. And they both were considered adults. Compare that to today, when people under the age of 18 have no legal standing as an adult, people under 21 can't decide to drink (or gamle in some states), and people under 25 can't be trusted by the insurance company to drive safely or be elected to the Representatives according to the Constitution. It's a cultural bias. As life expectancy progresses, the age of Majority is pushed later and later.
For a society where people can live to be 500 before retiring to live another 500 years in retreat, 100 years seems very short. According to the storybooks associated with D&D, elves are supposed to be much more far-sighted in their planning than humans. This level of maturity only comes with time. These same story books indicate that the younger elves are more rash and prone to not taking the long view on actions. Actually, they act quite a bit like humans. And this, as far as elven society is concerned, is a sign of immaturity.
An 18 year old elf is probably physically mature, at least full grown, just hasn't mastered being an Elf. I don't think that they'd seem retarded, or too slow to grasp the facts of a situation: they just wouldn't react with the necessary forethought. I think that Thornir's wife had the right idea, whether that elf is 18 or 70. (But granted, the 70 year old would be much more adept at adulthood thant he 18 year old would be.)
Just my 2 coppers,
Sparxmith