this is just my own personal opinion, but i think marrying someone your own age, or close to it, is ideal. it's nice to be in the same place in life at the same time, and your children would appreciate their older parent not dying when they're still relatively young.
also, generation gaps can be hard to overcome. my husband and i were a year apart. we grew up in the same era, had the same life memories... if you're 10 or 20 or 30 years apart, you would not be able to share those common memories. i am reminded of that line in the movie, Peggy Sue Got Married, where nicholas cage says of his younger girlfriend, "she thought the big bopper was a hamburger." that line always cracks me up. anyway, there is something very nice, even comforting, about sharing the same growing up memories with your beloved.
that's not to say it can't work out between couples with big age differences. many marriages do. and i would not let it keep me from marrying someone i loved who i shared much in common with. compatibility and having a lot in common is very important. this would include agreeing on matters such as faith, having/raising children, etc. that, and being committed no matter what, keeps a marriage strong.
married 27 years and then my husband died :(.