These size chart "ages" are just an indication. Every child is unique. Centimeters will always be centimeters, so just go by how tall your child is and you will be ok. If your child is in between sizes you can take the size bigger for tees and sweaters but I advise to take the smaller size for bottoms.
50-56: NEW BORN
56-62: 1-4 MONTHS
68-74: 4-9 MONTHS
80-86: 9-18 MONTHS
152-158: 12-13Y (adults size S)
164-170: 14-16Y (Adults size M)