Question: how old are mako and bolin?
Answer: Since Mako was 8 when his parents died and Bolin was 6 Mako is 2 years older than Bolin, therefore, since Mako is currently 19 Bolin is probably 17 or 16 1/2. That is an appropriate age for Bolin cause he dated Korra who is 17 years old. and sort of appropriate for Mako.