In a sign of the times as agencies begin to recover from years of cutbacks and hiring restrictions, the Air Force says that its work force is now “out of balance” — specifically, too heavily weighted with older, long-term employees, nearly half of whom are eligible to retire in five years. Other agencies are feeling similar aches. Air Force’s distribution of skills also is out of whack, with special concerns about the currency of skills in highly technical occupations. The agency is working on a three-part strategy that focuses on force renewal, force development and separation management — in other words, continued use of buyouts, early outs and other tools targeted at older employees. On the other end, it wants to simplify its hiring practices and emphasize internships and developmental training.