The 50-year-old Baby Boomers are coming! Eleven thousand a day, one every seven-and-a-half seconds for the next decade, they will reach that midlife landmark. Having done so himself, CBS commentator Geist (Monster Trucks and Hair-in-a-Can, 1994, etc.) offers his take on the apparently unexpected phenomenon of growing older. It's the startling receipt of an AARP membership card that initiates the author's comical ruminations about his condition. He covers aging--the humorist's classic material--in something life 50 short checklists and brief essays. Among Geist's complaints: He's contracted CRS, or ""Can't Remember Shit"" (his case seems confirmed by the repetition of a few favorite gags). He wants to wear a name tag for his own edification. His bawdy reportage segues to narcoleptic parties, maturing kids, health spas, trifocals, the music of John Tesh, incontinence, and the grand opening of a funeral home (where guests nibbled on finger sandwiches ""from the caterer, not the back room""). With particular attention to urology and his (or anybody's) libido, Geist seems to aspire to the post of Dirty Old Man, which is okay if it's funny. Happily, most of the time it is, with just an occasional lapse. Make what you will of his sex advisory: ""Just Keep It to Yourself. At this point why drag others into this ugly business?"" For the ladies, he has a few comments on Premarin and the fitting of fiftysomethings into bathing suits. Geist, of course, has an attitude: Gall Sheehy, he has concluded, is full of that stuff he can't remember (see ""CRS""). He covers his subject with an acerbic wit that occasionally calls for a large dose of Maalox. If the AARP card so affected Geist's spirit, what will happen when his Medicare card comes 'round? Still, this is way funnier than Modern Maturity.