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