There are many different opinions about how age factors into a relationship. Some people say it does not matter and others say it is everything. Some people are like me, sort of in the middle.
Age is just a number, or is it? You would think for example that if a man has been alive for forty five years, he would be somewhat mature and experienced in relationships. I guess someone with a rational mind might assume that. Well, experienced yes, mature, maybe not.
While the person might have experienced a lot of different things in their life, it does not necessarily mean that they have learned from them. Some people never grow up. This may be fortunate or unfortunate depending on how you look at it. However, it is a fact of life. If you date this kind of person you are likely in for a rocky relationship. I do not advise you to go for it. Maturity is more a matter of personality than age.
So to summarize I would say that while you do not want the age gap to be too significant due to practical reasons like how long the person might have until they die or at what age they will stop having sex and procreating. Also, lifestyle and cultural differences might emerge if there is a significant age difference. However, I feel that as long as you are within the ten year gap range, you are okay. Everything else is mainly personality differences. Personality is the main factor which determines the success of any relationship.
This is not to say that there are no exceptions. Those are always out there and I guess you should get to know your partner well and know what you are getting into before taking any chances with your life. Follow your gut. The heart wants what the heart wants in the end. It does not matter how ridiculous it may look to other people.