OAP,
Therein lies a question!
It all depends on which service or branch/trade you're referring to. One problem is that the state these days, classifies a veteran as anyone who has served in the Armed Forces for at least one day. The results are skewed therefore, because you include recruits who throw the towel in after a day, in a truculent fit, in the same way as an RSM/Lt Col/WO or Wing Commander with 22/30 years under their belt.
Many 'genuine' vets, those who we think of as having served a while after finishing training,
are affected adversely of their recent ground combat experiences (Iraq, Kosovo, Afghan, Bosnia etc) but are advantaged by better physical conditioning when set against the civvy population. The problem is made worse because many modern servicemen and veterans feel hamstrung and let down.
The traditional idea that a National Service/Cold War SNCO/WO was dined out and then bowlered off a unit, simply to keel over with a heart attack 6 months later doesn't really stand up to closer scrutiny these days. I know some young infantry vetarans who are highly eloquent; I'm not sure if they were 'different' before their service or if their subsequent experiences had an impact. This is a few years old but useful.
House of Commons - Defence - Written Evidence