At the 1920 Summer Olympics he finished fifth in the long jump final with a jump of 6.885 metres. At the 1924 Summer Olympics he finished thirteenth in the long jump with 6.72 metres, and at the 1928 Summer Olympics he finished fourteenth with 7.07 metres.
He also competed for the 4 x 100 m relay team which was disqualified in the first round of the relay event. He represented the clubs Fagforeningernes TIF and Torodd IF. 7.45 metres was the Norwegian record until 1934, when it was broken by Otto Berg. Aastad had previously held a record with 7.22 metres between September 1921 and August 1922.
lieutenant was broken by Sverre Hansen.
Aastad also held the national record in the 4 x 100 metres relay from 1920 to 1935, and in Swedish relay from 1925 to 1926. He participated in six international matches.
After the war, he worked as manager and accountant in the Norwegian Athletics Association from 1945 to 1949. He was later employed in Norsk Jungnerakkumulatorfabrikk.
From 1951 to 1952 he was a member of the elite sports committee.