The average lifespan of an adult housefly is approximately 15 to 25 days. Since they can complete their lifecycle in as little as seven to ten days, flies typically live between 22 and 25 days from egg to death. (wikipedia)
It depends on if you did use the lifespan or the time from egg to death. So if wee took 23.5 days as avarage for their full lifespan.
23,5 * 387 = 9094,5 Days
so if we belive that one year has 365 days (excluding leap years)
9094,5 / 365 = 24,916438356
that would conclude that he is 25.
BUT
we know
http://tv.boingboing.net/2008/04/07/tys ... earol.htmlit is said in this piece of information that he is 21 years old which was in april this year. soo
he is probably 22 years old. If this information is correct.
so that brings this to a conclusion
22 * 365 = 8030
as he states "I turned 387 in housefly years"
830 / 387 = 20,74935400
lets round this up to 21 that would say that he took not the full lifespan of a fly.