Complex sentence: By 1900, he was old enough to attend the Academy of Arts, and was one of the three students admitted that year; the two other sucessful applicants were his friends Ivar Kamke and Pontus Lanner.
Split into simpler sentences: By 1900, he was old enough to attend the Academy of Arts, and was one of the three students admitted that year. The other two who were accepted were his friends Ivar Kamke and Pontus Lanner.