Dani,
With you saying that he has a short nap, it definitely sounds like it is time to transition.
When transitioning you need to watch your lo's cues closely. You could try extending by 10 minutes at a time for the first few days and then a little longer.
You don't want your lo to get over tired, so need to watch his cues very closley. At the first sighn of tiredness you need to start your wind down routine.
HTH
Paula x