All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If you mean that your friend wants to marry this woman with the intention of divorce, then marrying with the intention of divorce is of two kinds:
First kind: To mention in the marriage contract a definite time period for marriage is forbidden, as this is the Mut'ah marriage (which is prohibited type of marriage contracts that specify a certain period for the contract).
Second kind: To have the intention of marrying for a temporary period without putting this as a condition in the marriage contract. The majority of the jurists do not forbid it, but some of them do.
At Islamweb our view is that your friend should not enter a temporary marriage because a Muslim would not accept a female relative of his to enter such a marriage.
Furthermore, what prevents him from marrying this woman with the intention of keeping her as his wife, as Allaah may bless this marriage and put much good in it? It might be that if he intends to preserve her chastity and be kind to her, he will be greatly rewarded. In addition to this, his marriage to this woman does not prevent him from marrying a second woman if he believes that he can be just between them as regards provision and spending the night with them equally. Allaah says (which means): {…then marry those that please you of [other] women, two or three or four.}[Quran 4:3].
Finally, if you consider that the difference of age is the problem, then this is not a deficiency in marriage as the Prophet married Khadeejah while she was 15 years older than him.
Allaah Knows best.