Much like any human life I'd imagine. Could be very short, could be very long. Heck, an Avatar could catch pentapox and keel over as an infant. Or he could die in combat, a lot of that happens I bet like the Ko incident five hundred years ago.

Well let’s look at this logically. When first learn about Kyoshi, Aang is 112 years old. It is said that Kyoshi lived at least 370 years as part of the air bender cycle. So when Aang was born, there is a 258 year gap between the birth himself and the birth of Kyoshi. That leaves three avatars to take the gap until we get Aang (Avatar A (water), Avatar B (earth), Avatar Roku (fire)). If we divide up that gap evenly among the four avatars, each has an average life span of 64.4 years.

The anomaly is that Roku was said to live at least 170 years ago when we first hear about him. Using the same logic as before, that means there was a 58 year gap between his birth and Aang's. In conclusion, Avatar Roku was at least 58 before he died. The variables I'm ignoring are that the sprit avatar sprit might be delayed from one mortal to the next. Also, the years I was using all had the key term "least", so that the avatars could have been much older. Also when I interpreted the term "least" I took that to been how long ago they were born.

See now thats fine and dandy, however Kyoshi was an Earth Avatar. So there would've been another Fire Avatar after her before the next cycle starts that my friend throws a wrench into the whole theory. But I do like your pretty accurate numbers so rework them and get back to me.

Ok I went back and recalulated it. Still using the same conditions as above I got this. If Roku live 170 years ago and Kyoshi lived 370, we have a gap of 200 years between the births of the two avatars. Including Kyoshi, we have to split up the those 200 years between five avatars (Kyoshi [earth], avatar A [fire], avatar B [air], avatar C [water], and avatar sword {saw a picture of him in one of the episodes} [earth]) So keeping that in mind the average age for those avatars is 40 years. That is a good long life for the ancient world.

Alright now for the other question. Was it from Kyoshi to Roku to Aang or was it the cycle in between them.

There was a whole cycle between them. I'll illistrate. Kyoshi [earth], avatar A [fire], avatar B [air], avatar C [water], avatar sword {saw a picture of him in one of the episodes} [earth], Avatar Roku, Avatar Aang. Did that clear it up?

Alright I guess that answer suits my needs thanks for the help Proessor.

It may be right but I don't think so because that would mean that they all died at the age of about 60 years old but that seems weird to me because Bumi is more than a hundred years old. Then perhaps these Avatars died in battles because this exemple proves that a normal guy might be able to live a hundred years old. And remember the cycle we saw in "the Avatar State" when Roku explained the problem of the Avatar State, Kyoshi was just before him. Soooo.......?

GAAAHHH!!!!! You must not have read all of my posts. First off, keep in mind that this is based on ancient history. Most people died young by our standards today. Bumi is just an anomaly in the trend that we have seen. Second, Kyoshi did not follow Ruko. If you look at the episode "Southern Air Temple" it show statue of Avatar Roku. Next to him is not a woman holding fans, but a man holding a sword. This logically means that that there was a whole cycle of avatars before Ruko. I will repeat the cycle starting with Kyoshi and ending with Aang.

Avatar Kyoshi [earth], avatar A [fire], avatar B [air], avatar C [water], avatar sword {saw a picture of him in the "Southern Air Temple' } [earth], Avatar Roku [fire] , Avatar Aang [air].

The average age for the Avatar Kyoshi, A, B, C, and sword is 40 years. This is justified using the math in my last post. Avatar Ruko is at least 58 years old using the conditions listed in my first post.