<P><B>Smile, and remember that being 50 won't be all that bad</B></P> <p>You may now expect a dirty weekend to involve nothing more exciting than cleaning out the garage, and you may find yourself being snubbed even by street peddlers. On the bright side, you can take delight in the fact that you will never again have to force yourself into groaningly tight fashion jeans—or pretend to like tequila slammers.