I believe licensed in EASA means runway, hardened, 800mtrs or longer with an instrument procedure(but I may be wrong).
No, there are lots of licenced grass runways throughout Europe and many runways below 800 metres. Netherthorpe Airfield (EGNF), Sheffield is a licenced aerodrome. It has two grass runways: 06/24: 553 metres and 18/36: 382 metres.
Nowhere can I find a reference that the airplane has to cross the DER at 50’ on take off.
No such regulation exists. If the aeroplane can perform better than the published minimum safe operation for a particular runway then you should do that and this is expected. How to calculate the minimum take off roll and the total distance to achieve 50 ft, for various conditions, is found within the aircraft's Flight Manual/POH.