What is a good 5k time for a 55 year old male?

To be in the militay, you need to run two miles in 15:54 (at age 18). At age 30, in the military, you need to run two miles in 17:00. So if you are very fit, I'd say an 8.5 minute mile. If you are not fit or are trying to get fit, maybe a 9-10 minute mile.