Size length: 160 inner length 16cm (25-26 yards) 2.5-3 years old
170 inner length 17cm(27-28 size) 3.5-4 years old
180 inner length 18cm (size 29-30) 4.5-5 years old
190 inner length 19cm (31-32 yards) 5.5-6 years old
200 inner length 20cm (size 33-34) 6.5-7 years old
210 inner length 21cm(34-35 yards) 7.5-8 years old (reference age)