Yes, he's definitely too young to be dropping his nap yet.
What time have you been doing BT when he doesn't nap? The key is to do a as early a BT as possible.
If he's not napped for 5 days now then he will be very OT. I think I would try giving him a nap much earlier than usual (like 11/11.30am)...if he's very OT then you will more than likely be missing his sleep window if you have been trying to get him down at his usual nap time. Make his bedroom as un-interesting as possible by storing away all toys etc that can distract him from going to sleep. Also it would be worth trying a bit of a longer wind-down so that he is as calm as possible before he goes down.
If this doesn't work then I think you might need to try APOP'ing a nap in car/buggy just to try & get him caught up a bit (not ideal, I know but I think you need to try & curb the OT as much as possible).