Twenty-five years ago, most men in the Tampa Bay area married by age 35. But since 1980, the number of never-married men 35 to 55 has jumped sevenfold. ST. PETERSBURG - On the eve of his 50th birthday, Robert Mendenhall was trying to decide whether to spend the big day with someone new or with his ex-girlfriend. She had held his interest the longest: eight months. Mendenhall, who works in regional sales for a roofing and window company, hangs out with half a dozen never-married men in their late 40s and early 50s. They are successful at their jobs, keep...