Other than the requirement that both parties are of legal age to marry, there is no other age related requirements or rules for a marriage based I-130 visa petition.
That said, you should be aware that having seen hundreds or thousands of marriage greencard cases, most of the cases that had problems were where the husband was much younger than the wife. The fact is, in Anglo-European culture men almost never marry a woman who is 15-20 years older than him. So when the USCIS receives a case like that they are very skeptical. They basically assume it is a fraud to get a greencard.
On these kinds of cases the couple needs to get much more proof than is normally needed. The couple should have evidence that they have known each other for a long time, should have evidence to show that their finances are completely intermeshed (not just a joint account, but other things like retirement accounts showing the spouse as the surviving beneficiary, a notarized will showing the spouse to be the majority legatee, joint leases or ownership on cars/houses/etc., joint names on bills like cell phone/electric/etc., joint health insurance, life insurance with spouse as beneficiary), not all of those things are necessary, but you get my point.
Should have lots of pictures showing the family together, especially if one or both of you have children photos should show that your children have met each other. Also if one of the spouses has already petitioned for a prior spouse to come here, it will look bad. I know that in a few cultures it is common for a younger man to marry a much older woman. If you both come from that culture you can submit background evidence showing that this type of marriage is normal for you. (That actually helps, believe it or not).
However, if you have children together, or if you were married in your country before you ever came to the United States, then your case will be much easier. If you are not married yet and plan to go to her country to meet and marry her your case will be very difficult.
