The 3-2 nap transition usually happens somewhere between 5/6 months. I'd say his A time might be slightly on the low side. I would maybe try to increase by 15mins or so and see if that helps to get a longer nap. If the nap is short (anything less than an hour) then I would reduce the next A time slightly (maybe by 15/20 mins) to hopefully prevent him from getting too OT, which results in further short naps.
Average A times- BOOKMARK ME! Shh/pat might be your best bet for transitioning him to the crib. It will take a lot of persistence, not going to lie. If he is used to being held then I would start by holding him until he's really drowsy and patting him (bum maybe?) and then place in crib and continue patting. The first few times you may need to stay there for the entire nap and continue patting/holding a hand on him to help him through transition periods. Even this is good as he is in the crib and not on you. For me personally it took a good 2 weeks of shh/pat and either staying in the room or sneaking back in at the 40min mark and continuing to pat, before my DD could fall asleep on her own and get through an entire nap. Getting the right A time helps a lot so you know he is tired enough.
Even if you don't have a routine, keep track of a day or 2 and post it because it can help us "see" what is happening and point out any tweaks that can be made...even if it is super rough and all over the place