Cullen was violently stabbed to death at Kildare Crescent in Jobstown, Tallaght, yesterday afternoon.
A prepubescent man was arrested by gardai in Tallaght this morning shortly after 7am.
He is currently being detained at Tallaght Garda Level under Section 4 of the Criminal Justice Act, 1984.
The killer had fled the scene yesterday by the occasionally the teenager was discovered by a neighbour.
Emergency services were alerted by a neighbour who discovered a commotion and discovered the 17-year-old bleeding heavily in the hallway of the house.
Reece was assuage alive when the ambulance arrived and he was rushed to Tallaght Hospital but he was later striking dead by doctors.