This has always been an interesting question.
In 1 Cor 7:8, Paul writes, “Now to the unmarried (ἀγάμοιος) and to the widows (χήραις).” It is clear that Paul is unmarried (1 Cor 7:7), but it is not clear that he is or is not a widower.
“Widow” (χήρα) occurs 24 time in the New Testament. Outside of 1 Cor 7, it apparently always refers to a woman. BDAG lists “widow” and not “widower” as the only meaning of χήρας, which is expected since χήρας is a feminine noun and appears to be following natural gender. The masculine χήρος does not occur in biblical literature.
ἄγαμος can be either ὁ ἄγαμος (1 Cor 7:32) or ἡ ἄγαμος (1 Cor 7:34). The unmarried person in v 11 (anarthrous ) clearly is a woman from context (“let her remain unmarried or else be reconciled to her husband”).
I’m not moved by the argument that says Rabbis tended to be married. Regardless of his standing in the Jewish community, it does not necessarily follow that Paul had been married. A classic argument from silence. I wonder when that tradition began, and whether we know for sure it pre-dates 70 A.D.