In Kendo, age is not important. However, the reason for that same contradicting restriction may be because of other issues.
For example, In some places they pay for personal insurance(If you get injured during practice) and it's divided in two groups. one is for 15 and younger kids the other, is made for 16+.
And since some dojos don't have enough kids(or none at all), they don't bother to get the one for 15-(that's how it is in Sweden). If that's the reason I recommend getting a group of 15- kids and ask together. (^.^)-b