From an enfant terrible, once hailed as a new Bob Dylan, to a wary but not too grumpy older man, Loudon Wainwright III, now 68, has stayed the course for well over four decades, charting his life and times with pungent light verses and biting turns of phrase. As a folk singer-songwriter, he has proved that a sharp sense of humor can make for verses more durable than earnest self-examination. You can’t whine about the aging process but you can confront it and soften it with laughter.