First of all, as the show is entitled Age of Love and runs on the premise of age being the central dividing characteristic, thus, this rule must be strictly implemented. Season 1's cast was not held tight by this rule, as the difference in age was not equal between the 20+ Kittens and the 40+ Cougars. Mark Phillippousis, who is 30 years old, would naturally be closer in age to the 20-something ladies than to any of the 40-something women. He was only equally distant in age from Megan, 21, and Jayanna, 39.
True love may be able to transcend a factor such as age, however, one must take note that a man can't immediately be love struck with one in the selected 40 contestants. If there aren't immediate sparks, then people tend to move on to other secondary factors such as common interests, similar outlook, and shared future goals.
When it comes to Mark's maturity level, he was also in tune with the 20-something ladies. In fact, his past relationships had been with younger women, and he admits always having been compatible with younger women. The show then became pretty predictable that Mark would choose one of the ladies over the women.
Having a slightly older man would make the game more interesting, especially if he has children, as some of the Cougars were divorcees with kids, thus having a lot more maturity and experience in life. In addition, if the bachelor already has kids of his own, there would be less pressure on the woman to fulfill that expectation. As harsh as it may seem, a bachelor with kids might have more emotional maturity that Philippousis was lacking.
No official word out yet about Age of Love's direction after the first season, but if ever it gets renewed, viewers hope that NBC would listen to their feedback just to make it a bit more realistic.