In the 1993 movie “Falling Down,” Michael Douglas plays an angry white man whose midlife crisis has him nearly foaming at the mouth. Appalled by a brutal traffic jam and disorienting changes in his world, he flips out in a Korean liquor store, tangles with the homeless and construction workers, amassing an arsenal as he tries to make his way across town. His breakdown leaves casualties, makes the news — everyone notices. An eloquent latter-day equivalent, Noah Baumbach’s “Greenberg,” shows a meltdown going differently: The protagonist’s moment of crisis: Shrouded in an oversize ski vest, he wanders alone, quiet and pathetic, existentially lost on the edges of a party. Even his best friends don’t notice.Created nearly 20 years apart, the films illustrate two different generations hitting middle age. People heard it loud and clear when the baby boomers crossed over to midlife – you couldn’t avoid it. Radio talk show hosts probed into the transition, newspapers described boomer women coping with crow’s feet and men reclaiming their vitality in tribal drum circles. For the generation born after – in the ‘60s and ‘70s, raised by television like no previous generation and with the divorce rate skyrocketing during their childhood years — there is no media watch broadcasting their new trajectory. Few have even noticed that this small, notoriously rebellious clan – those born roughly between 1965 and 1980, which means about 46 million Xers versus 80 million boomers — has entered middle age. It’s a transition that, until now, has been captured, mulled over and ridiculed for each generation for more than a half-century. But not this time.