OP, You are not alone on this. Check out this link to a chart that shows a man's age vs the age of women who look best to him
http://www.businessinsider.com/dataclysm-shows-men-are-attracted-to-women-in-their-20s-2014-10
Don't get down about your age. You've earned the wisdom that comes with age. Use that to your advantage. Have the mindset that women must earn the right to spend time with you, not the other way around. Don't ever get down about not being married either. Due to divorce laws, marriage is a raw deal in Canada / US. There's a good chance you would find yourself in the majority - over 60% of couples in populated metropolitan cities will divorce. And that doesn't mean the other 40% are happy. Just together...sometimes for the kids, family shame, family inheritances, etc. If you were to combine divorces and unhappy marriages into the mix, you are looking at closer to an 80% failure rate. Don't take my word for it. Do some research.
Be happy that you are single and 40. You are free to do whatever the hell you want!!! By all means, short or long-term date or see SP's (or both) but don't get married. if you are lonely and want companionship, friendship, etc. then get more male friends. Golf, fish, hunt, play squash, attend sporting events. There are lots of guys in the same boat as you and the bonus is that increasing your social circle will help you appear more attractive to women.