It can take a few weeks to establish a DF, I would try it a bit earlier than 11pm and see if catching him in a different part of the sleep cycle helps. He may still wake for 1 nightfeed for a while yet plus 4 months is big growth spurt time so he will be looking for more calories.
He's not too old, but give it a couple of weeks and if he's not taking it or it's making no difference I would stop trying. Some babies just don't take to it whatever age, neither of mine would take a dream feed so we just fed when they woke and got back to sleep as soon as possible.
HTH!
Laura