What length necklace for a 13 year old?

[Deminism]

It is a gift so hard to find out. Am hoping it is a necklace they will want to keep into adulthood - should I therefore go for adult length 45cm or child length 36 cm?

Shorter length or it will be too awkward for them to wear. If they choose to wear it as an adult, the chain can be added to or changed.

36 otherwise too awkward