said by danawhitaker:
According to Wikipedia, he was born in 2511. I'm not terribly familiar with the Halo universe, aside from a smattering of watching Red vs. Blue back in the day and following the franchise through friends who played, so I'm not comfortable giving an answer beyond that. So I guess if you know which year(s) in the timeline Halo 4 is set in, that should help narrow that down.
Also according to Wikipedia, the events of Halo 4 are set in the year 2557. Thus, if you use the 2511 date, he would be about 46 years old. However, with all of the modifications (cybernetics and medicinal), plus the hibernation from the cryo-sleep the Chief has been in repeatedly from the many travels he has done aboard ships, there really is no way to accurately say how he has aged. John (Spartan 117) may be the equivalent of a 21 year old, by our standards.--
From Psychonauts -
Lungfish Civilian: (describing Goggalor) He's impervious to bullets! ... and love!