I only give my males 2 females per season. This keeps them going strong all season and then some.
Also feeding is essential too. If a male is young and stops eating during breeding, I stop his breeding till he eats again.
My main male is an 09 but a picky eater. He hasn't ate in months and I'm stopped breeding him early because he was losing weight. He went from 550 and now is 450. Hasn't ate in about 4 months now.
All of our males used were between 700g to 1200g. We also only used like one male to 2 females. The males were put in with a female for a week and then off for a week. This rotation continued untill the females stoped responding.
I used one male to 4 females which I usually do but a lot of my males were 450G-550G as I was excited to try and get them going.. May have shot myself there