Answer

When angels take on visible form, they always appear as young men. Demons are fallen angels, so they still have that same ability. When angels appear in visible form, they can do many physical things, such as rolling away the stone from Yeshua’s tomb. Hence, they can also function as young men, which allowed them to have sexual relations with women and thus produce the Nephilim, a race that was neither human nor angelic but a race of Nephilim. Ultimately, this race was destroyed by the flood of Noah.

Book: A Study of the Angelic Realm: Angelology, Demonology, and Satanology