Love Between Older Rats?

Hi! I'm contacting you because I have a quick "rat" question. Right now, I have a male hoodie who is about a year and a half old, and, though very active, is definitely past his sexual peak. His name is Gregor, and he is, in all ways, the perfect rat. Loving, smart, friendly, etc. What I want to know is, if I wanted him to be the "father" of a litter of rats, and if I were able to find the perfect young female sexy thing - not that I know what rats consider sexy - would he be able to perform sexually, or is it simply a matter of that his body doesn't do that anymore?

Thank you so much,
Holly, Gregor's "Mommy."