Can a older male gerbil get a younger female gerbil pregnet?

Yes. Male gerbils, no matter how old they are, can impregnate female gerbils. Most female gerbils can no longer conceive after 2 years of age. Either way, it's never wise to put a male and female together unless you intend to breed and provide for several litters. Gerbils are not easy to find homes for.