Three years ago, the U.S. Army just raised the maximum age for new recruits from 40 to 42. This was expected to bring in, at most, a few hundred additional recruits a year. The army needs about 80,000 new recruits each year. Four years ago, Congress allowed the Department of Defense to accept recruits as old as 42 (the previous maximum was 35). The number of older recruits grew year by year, and the number over 35 now accounts for five percent of the annual total.
In basic training, the staff has come to depend on these older men (nearly all are male) to help the younger recruits. With age comes maturity and wisdom, and the older recruits have fewer disciplinary problems and are easier to train. When the older troops reach their units, they continue to add stability and provide a larger pool of low ranking soldiers that can be depended on. The older troops also have more skills, which also prove useful.
Since 911, there have been thousands of older men, and women, wanting to enlist. When, in 2006, the army raised the maximum age to 40, and they soon brought in 1,065 new recruits older than 35. However, 65 percent of those older recruits were for reserve units. The older recruits have to meet the same physical and mental standards as do 18 year olds. But advances in medicine and physical training technology has produced a lot of very fit 40 year olds, and most of them are not professional baseball players. Despite that, older recruits tend to wash out of basic, for physical problems, at a slightly higher rates. Older injuries, particularly from school sports, tend to reappear when you get older, like in your late 30s. High school and college football players know all about this.
But with so many reserve units being activated and sent overseas, these older troops got to prove their worth in combat zones. On the down side, older troops are more prone to PTSD (post-traumatic stress disorder). Israel was the first to note this PTSD angle after the 1982 war in Lebanon. This conflict went on longer than previous wars, and used a larger number of older reserve troops. The older soldiers, especially reservists, tended to be more prone to coming down with PTSD. This was probably due to the fact the full time soldiers are constantly conditioned to deal with stress, and younger men have fewer other responsibilities to distract them.
Moreover, what is known, often derisively, as "military discipline," helps because such practices reduce stress and panic during combat. The younger troops depend more on discipline to get through combat, while the older troops use more of their more extensive life experiences. Apparently the discipline angle is better at reducing the chances of coming down with PTSD. Israelis also began intensive research into PTSD around the same time, and have led the field ever since. The U.S. also found more PTSD cases in reserve units, and among older troops experiencing combat for the first time. But the benefits of having older troops in the junior ranks has been a generally positive development.