THE MEN AND THE GIRLS By Joanna Trollope (Black Swan, $102) WHEN males write about older men with much younger women, they tend to get carnal. The swain may be an old fool or one of the last great romantics, but the essential thing is that he has conquered - however briefly - young, rejuvenating flesh. Now here is a woman writing about two men in their early 60s married to women young enough to be their daughters and the view, as might be expected, is quite different. Ms Trollope is not concerned with the physical, other than to make it plain that Kate and James, and Julia and Hugh are perfectly compatible. They have been brought together by love, not lust or greed - and yet things go desperately wrong for them. A minor accident triggers the emotional avalanche. Absent-mindedly driving without his spectacles one night, James knocks elderly spinster Beatrice Bachelor off her bike and is overcome with shock and shame. ''The worst of it,'' he tells Kate, ''was that she was so vulnerable, one of those frail old academics with a bun.'' To which Kate, normally so warm and understanding, replies with chilling contempt: ''You stupid old man.'' Just four words, but nothing will ever be the same; not for James, Kate or the two - one so young, the other so old and both difficult - who depend on them. To the well-preserved Hugh, James' best friend since their undergraduate days at Cambridge, late-life crisis seems remote in the perfect home he shares with the perfect Julia and their cherubic twin sons. Then the axe falls and Hugh, popular TV host, is suddenly yesterday's news just as Julia's star is rising. As the men and the girls flounder, it is the tough, wise Miss Bachelor who brings fresh possibilities and bridges many, if not all, the gulfs. In Ms Trollope's civilised middle-class world, with its Aga stoves and engaging eccentrics, there are no devastating tragedies and even the most bitter loss emerges as a sort of triumph.