Nils was educated in the family trade of woodworking from an early age, and his earliest preserved work is a wooden sculpture of Bishop Arne Fjellbu, made when Aas was 16 years old. After graduating from secondary school and after a short stint in military service, Aas applied to the Norwegian National Academy of Craft and Art Industry in 1954 at the age of 21; his older sister, Marit, had started at the school two years earlier. His father marked the occasion by making a suitcase of wood as a farewell gift to the son. Aas studied at the school from 1954–58, notably under Arne Bruland and Ivar Bell. Bell taught Aas calligraphy but ultimately pushed his pupil towards his eventual career as another type of artist, commenting "I think you are three-dimensional"; Aas took the advice and enrolled in sculpture classes the next term. Upon leaving the institute, Nils went on to study under sculptor Nils Flakstad from 1958-1959. At the end of 1959, he accepted work with Per Palle Storm.