The Book of Guys by Garrison Keillor Faber $255 MIDDLE-AGE doesn't suit Garrison Keillor. The prairie philosopher and much-feted humourist has long used the slight sense of impending doom that goes with being fortysomething to add an extra dimension to his highly amusing tales of life in middle, largely rural, and often middle-aged America. Keillor is a radio man. For 15 years his show, A Prairie Home Companion, has been broadcast to the Mid-West. The books it spawned, especially Lake Wobegon Days, offered a style that easily transferred to the written page, to a wider audience, national celebrity and comparisons with Thurber. Now Keillor has turned 50 and the bewilderment with life always present in his writing has come out full force in The Book of Guys. The wit and sparkle are still there; some of these 21 essays are as funny as anything you will read today. But, with the helplessness of the American baby-boomer male as his theme, there is an edge here that is unmistakable. Keillor believes his sex is in trouble and there is precious little we can do about it. ''Girls had it good,'' he writes in his introduction. ''They got to stay indoors. Boys ran around in the yard with toy guns going kksshh-kksshh, fighting wars for made-up reasons, while girls played with dolls, creating complex family groups and learninghow to solve problems through negotiation and role playing. ''Which gender is better equipped, on the whole, to live an adult life, would you guess?'' No prizes here for the right answer. ''Women don't decorate our lives any more,'' he grumbles further on. ''They are intent on expanding their own opportunities to be miserable, by going into law and business and becoming as corrupt as men.'' Surprisingly this is not a sexist argument, unless you count man as the victim. Keillor believes that, under the new rules, his sex simply hasn't a prayer. He illustrates this sense of hopelessness with a succession of stories ranging from his own experiences at an overnight male-bonding session where ''desperate low-lifers tell you a long story for a five-dollar loan, guys who everything unfortunate has happened to'' and gently freeze in their own self-pity as the temperature falls at their woodland meeting place; to the much funnier Mid-Life Crisis of Dionysus, where the immortal God of wine turns 50 and, to his eternal shame, loses his appetite for orgies; and Lonesome Shorty, the cowboy who wants to leave the range and settle down to a normal life with a loving wife amid a set of fine-boned china and blue-dotted Swiss curtains. All through The Book of Guys, Keillor's men are victims. Some manage to survive after a fashion; others like the original Don Giovanni, caught in early old age eking out a living as a small town cabaret act, don't. It all fits the Keillor philosophy. Modern man is expected to ''bake a cherry pie, go play basket-ball, come home, make melon balls and whip up a great souffle, converse easily on intimate matters, participate in recreational weeping, laugh, hug, be vulnerable, be passionate in a skilful way and the next day go off and lift them bales into that barge and tote it.'' We don't stand a chance.