Don't know about the Navy, but when I was in ('68-'72) the Army Nike Hercs, all the lifers looked at least 65 years old, while still putting in their 20. The service seemed to age them quickly.
I went from basic at Ford Ord, CA (the Land that God Forgot) to AIT at Fort Bliss, Texas. Then on to a Missle Track Radar job near Travis AFB. Got an early out as E-5 in Dec.'71.