The official guidance is "as often as he wants to day and night"
Mine were on 4 BFs a day by this age plus 3 solid meals. Ds1 dropped to 3 BFs quite soon after he hit 12-13mo. Ds1 was older, maybe 20mo when we dropped to three. We dropped the rest one feed at a time and we were all done at 26mo for both.
Going by his adjusted age I'd say at least 4 times to get all the nutrients he needs. You're looking to get about 20oz in so it's unlikely he would get that from any less. Remember milk is his main source of nutrition until 12mo. If he didn't want it that is different but if he is happy with 4 feeds I would stick with them until at least a year.