Being with someone much older than you could bring problems if you both want children. According to researchers from Mount Sinai School of Medicine and the Institute of Psychiatry, children with older fathers have an increased chance of being autistic, due to genetic mutations in aged sperm cells. There is also the possibility your significant other may not live long enough to see your child grow up. Physical mobility also decreases with age, meaning he might have a harder time looking after the children. You will have to analyze these possibilities and decide if they are worth the risk or not.
Dating an older man also brings the possibility your personal views will collide. For example, a woman who is in her late 20s is usually beginning to discover who she is. A man in his 40s, however, has had 20 years more than the woman to figure that out, and usually has. As a result, you both may want different things from a relationship. There may be compatibility issues between you and him. You also miss out on being with a person who is at the same life stage as you. Therefore, it is important you both come to a consensus on what you expect from the other in the relationship and stick to it. Move on if you cannot.
If you grew up without a stable father in your life, you may subconsciously end up seeing an older man as a replacement. He may also view you as the daughter he never had or wants to have again, if he has an adult daughter and wishes to relive raising her again through you. Your relationship could end up being more like a father and daughter one than a romantic one where both parties are equal. Again, it is up to you to make sure you do not end up seeing an old man as a father figure when you are dating. Look for a figure in other men, such as an uncle or family friend.
If the age difference between you and the older man is 10 years or more, that may indicate that he has troubles committing to women his age. He could be dating you simply as a way to feel young again or to have children. Make sure the love between you is genuine and not based solely on superficial issues such as these.