All of my babies hatched at 65-70 g last year and started off with large hoppers/rat pinks. There is no reason, in my opinion, to start a healthy ball python with anything smaller than a good sized hopper mouse. I prefer starting all of mine on rats if they will take them.
Feed him every 5 days or so and increase prey size as he grows. I switched all of my babies to every 7-10 days once they started taking weaned to small/small rats. This varies depending on how fast they grow, but it is usually around their first year old.