The other night, after watching the film Avatar, I was thinking about the possibility of real ET's somewhere in our universe. Holywood usually depicts them as only slightly more, or less, advanced than ourselves, but statistically (unless most intelligent races eventually self destruct) our distant neighbours should be millions, or even billions of years more advanced than ourselves. So, assuming a liferorm somewhat like ours, when did conditions first exist for intelligent life to evolve in the universe, and what should be the average age of any real ET race we encounter?