You could look on Craigslist for your area for exactly what you need. I don't think they would need to match his age, but old enough (big enough) to run from him if they have to, and old enough to stay outside.For getting him some females now would they need to match his age? Or ducklings will do and they will grow in to it?
I will have to shop around as I don’t believe they sell them sexed.