Men vs. Women
In general, women tend to mature faster than men but this is not a steadfast rule. A person's maturity also depends on life experience. It has long been considered socially acceptable for older men to date younger women because of this generality, but modern women are now dating younger men. If you are compatible with another person and find each other attractive, age difference should not be that big of a deal.
With the developments and changes in modern technology evolving at a pace faster than ever before, generational gaps can often be more significant for people born in the 1990s or later, compared to generations born before the Internet. When dating someone with a large generational gap, you may find she has never heard of many of your favorite movies or musical artists and vice versa. This can be a disadvantage in the sense that you may have less in common, but an advantage in the sense that you get the opportunity to introduce him to your favorite things.
One of the benefits of dating someone who is older or younger is that you probably don't share the same pop culture tastes and have the chance to discover new things. Dating someone who isn't your age can also force you to step out of your comfort zone and do activities that you wouldn't normally because it's not relevant to your age group. Dating someone older means you have more of a chance that he will be cultured, educated, stable, successful and secure in himself. Dating someone younger means you will have more of a chance that she will be fun, adventurous and full of life.
When you share a significant age difference with someone you are dating, you may not be at the same stages in life--which can be a serious problem. If one of you is ready to settle down and have a family and the other has already done that, you may find that your compatibility doesn't override your needs in life. On the same note, if you are older and dating someone younger, he may not be ready to settle down and commit.