Gustaitis was born in the village of Obelinė, in Javaravas county, in the Marijampolė district. He attended high school in Yaroslavl, and from there studied at the Institute of Engineering and School of Artillery in Petrograd. After joining the Lithuanian Army in 1919, he graduated from the School of Military Aviation as a Junior Lieutenant in 1920. Later that year, he saw action in the Polish-Lithuanian War. By 1922 he began to train pilots, and later became the head of the training squadron. He also oversaw the construction of aircraft for Lithuania in Italy and Czechoslovakia. Gustaitis was one of the founding members of the Aero Club of Lithuania, and later its Vice-President. He did much to promote aviation among the young people in Lithuania, especially concerning the sport of glidin