Well, it's not a disorder, but, If Dr. Phil or somebody would put in his two cents, he would probably say something like, the subject may have not had his mother in his life or his mom died at an early age. So, to compensate for not having a mother in his life, he turns to older women to fill that void. Vice versa for women as well, where they didn't have their fathers in their lives. They too turn to younger men to fill that void. By the same token, women who had that ugly duckling syndrome when they were younger, couldn't get guys in high school. So, to compensate for that, they turn to younger men, because they couldn't get younger men when they were young themselves, or quite possibly, the parents were so controlling, they weren't allowed to date when they were younger or simply didn't have time to date when they were younger, because of career or education issues.
So, from a psychological perspective, there it is, in a nutshell. So, it's all about the compensation to fill the voids, but, hey what do I know. I never finished college and I'm not doctor Phil. So, just go for what you want.