Yes, a private pilot's license (PPL glider) is required to fly gliders. OP probably meant that they were considering adding a rating for powered airplanes (PPL

Yes, a private pilot's license (PPL glider) is required to fly gliders. OP probably meant that they were considering adding a rating for powered airplanes (PPL ASEL - airplane, single-engine, land). Alternatively perhaps they mean that they took some lessons in a glider as a student pilot and considered going further and getting the license.