11 1–2 mo 12 2–3 mo 13 3–4 mo 14 4–6 mo 15 6–8 mo 16 1–3 mo 17 3–6 mo 18 6–9 mo 19 10–12 mo 20 15–18 mo 21 1.5–2 yrs 22 2–2.5 yrs 23 2.5–3 yrs 24 3–3.5 yrs 25 3.5–4 yrs 26 4–4.5 yrs 27 4.5 yrs 28 5 yrs 29 5.5 yrs 30 5.5–6 yrs 31 6 yrs 32 7 yrs 33 7.5 yrs 34 8 yrs 35 9 yrs