Aaltonen was 1912-1924 three -time Olympian. Making its debut at the Summer Olympic Games in Stockholm in 1912 he reached the semi-finals of both the 200m breast, as well as over 400 meters breaststroke. Eight years later, at the Summer Games in Antwerp, he won over these two routes, the bronze medals. For the last time he went - now 33 years old - at the Summer Games in Paris in 1924 at the start, but did not get over 200 meters breaststroke on the lead out.
His two medals remained until 1992, the last medals in swimming competitions for Finnish athletes.