Alexander Skarsgård was 7 in Åke and His World when he played the character 'Kalle Nubb'.
That was over 40 years ago in 1984.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
Today he is 47, and has starred in 53 movies in total, 47 of those since Åke and His World was released.
In Åke and His World, I think Alexander Skarsgård looks: