Can I fix his papers even though he older than me and what do I do to get it fixed?

The fact that he is older than you should not prevent you from filing a petition for your boyfriend, once you are married. However, depending on how he entered the U.S. (with a visa, entered illegally, etc.) he may have to go through consular processing in Mexico. Consular processing can be complicated and I strongly suggest that you contact an experienced immigration attorney for a face-to-face consultation and give him/her all of the facts surrounding your situation. (S)he would then be in a better position to analyze your case, advise you of your options and, if possible, make sure that the necessary paperwork and documentation is properly presented so as not to delay the process.

If you get married and he's otherwise eligible, you can begin by filing certain forms and supporting documents with immigration.