Jealousy is another issue. Sure, any of us can exhibit the green-eyed monster, but in large-age-gap relationships, this is more of a factor. In my experience, Tom was terribly jealous about me being surrounded by guys my own age when I was in college. Over and over again I had to reassure him the 20-somethings discussing beer pong and porn really did nothing for me. I told Tom he didn't need to worry about me leaving him for someone that was my own age. Having staggering amounts of sex with him certainly helped.
But by far the biggest factor in a relationship like mine is baggage. Are you ready to deal with your boyfriend's children? What about his ex? You must understand that an older man led a lot of life before he met you and accept his past to make your future together work. My advice: don't get hung up on the paths he took earlier in life. Focus on your life as a couple and what you want to achieve together.
If you're in a May-December relationship or contemplating one, just remember that, like any relationship, it takes compromise and compassion to make it work. When people look at Tom and me, maybe they see our age difference, but hopefully they just see a happy couple in love.