I never finished my Eagle. I left Boy Scouts at the Star level in the 70's.
My son crossed over from Webelos at 10 1/2 and in fifth grade with his Arrow of Light. He currently has 37 merit badges including all Eagle required. Just got his project approved on July 24th and is in the process of gatheirng the materials needed to complete. He is looking at finishing his project in late August early September, and if he meets this deadline will most likely have his Eagle BOR in October or November (Our District only conducts Eagle BOR's on the 2nd Thursday of each month).
If he completes in October it will make him 15 Years and 1/2 month. so basically, he will make Eagle in 4 1/2 years. He will also be the third Eagle Scout from our Troop that is now 6 years old.
Yep, I was one of those that just finished before I turned 18. Could I have done it sooner? Of course, but there were lots of things going on and I did them, but still planned to finish it -- and did.
I crossed over from Webelos on February 22, 2002(age 10 1/2) and my Eagle BOR was on April 19, 2007(age 15-almost 16) . So, that's just over 5 years. But, if you count Cub Scouts, it was more like 9 years.