Sex is not everything in a marriage, but it is indeed a primary and very important part of it. Sexual incompetence is grounds for divorce.
We have numerous narrations and rulings on this topic as well. A man asked Imam al-Sadiq (a.s.) about a woman whose husband was incapable of intimacy, and whether she should leave him. The Imam (a.s.) answered, Yes, if she wants to leave him. [al-Tahdhib, vol. 7, p. 431].
That being said, in regards to this specific question that has been asked, if there was such a huge age difference between them, why did she get married to him in the first place? Did she or her family not think of these things when they first got married? Can the problem be solved through medication?
In any case, the wife does have the right to request a divorce if she chooses to do so.
And Allah knows best.