DS just turned 7 months and is a major catnapper. He takes 3-4 40 min naps a day. Is there a trick to get him to extend his naps and only take 2? Or is this something that will come with age?

We have to leave the house at 11:30 & 2:30 to drop off/pick up big brother from school. He goes to bed at 6pm with two wake ups and gets up 5:30/6am. If he only has 3 naps he goes to bed early.