13 – 15 = 1 months – 3 months
16 – 18 = 3 months – 9 months
19 – 21 = 12 months – 18 months
22 – 24 = 2 years – 3 years
25 – 27 = 4 years – 6 years
28 – 31 = 7 years – 8 years
32 – 35 = years  – 10 years