Question

Six years ago my son was one-third my age at that time.

Answer 1

m - my age

s - son's age

$s-6=\dfrac{m-6}{3}\\s+6=\dfrac{m+6}{2}\\\\3s-18=m-6\\2s+12=m+6\\\\m=3s-12\\m=2s+6\\\\3s-12=2s+6\\s=18$

He's 18