Max weighed 3 kg at birth. After a recent doctor’s appointment, his parents were told that Max is developing normally; he now weighs 6 kg. How old is Max?

Max weighed 3 kg at birth. After a recent doctor’s appointment, his parents were told that Max is developing normally; he now weighs 6 kg. How old is Max?
A) about 3 months old
B) about 5 months old
C) about 8 months old
D) about 12 months old