DP is 42. I'm 30. I think he's at a great age, still young and fit enough to run around after DC's (9&7), but wiser and more grounded than a lot of men my age. The novelty of people commenting on his 'young missus' still hasn't worn off!
My sister is 43 and, again, still looks young, is healthy and happy. 40-something sounds old, but it's really not!