Age appropriateness is a frequent consideration of potential dating partners. In most cases, people will claim to prefer a partner close to his/her age, but in practical applications this isn't always possible.
There's no right or wrong answer about age differentials. Age can (and does) play a role in a person's personality and function in a relationship, but it's not always a perfect indicator. A couple could be 10 years apart in age but be in sync mentally and emotionally, while a separate couple could be identical in age with hundreds of problems.
Nevertheless, there are some common problems that come up when two partners differ vastly in age.
Younger Dating Older
Younger people sometimes find it difficult to date older individuals because of a difference in priorities. Older individuals tend to focus more on conservative life elements, such as careers and families, while younger individuals are more focused on fun. This isn't always the case, of course, but it can cause tensions when selecting evening plans or talking about the future.
Older Dating Younger
Older individuals might find it difficult to date a younger person because of the latter's emotional immaturity. Older people have been through far more life stages, and may find younger people naïve or ignorant to certain elements of life. There can also be a financial gap between the individuals, making it stressful for both parties when going out or trying to live together.
How Different Is Too Different?
There's no way to tell whether someone is "too old" or "too young" for you until you meet them and get to know them a little bit. Ultimately, the decision needs to be based on your own personal feelings, not what society expects of you, and not based on stereotypes.