Note [u1]: The data item for those aged 16 is based on between 10 and 24 responses and is categorised as being of low quality.
Nodyn [u1]: Mae'r eitem ddata ar gyfer y rhai 16 oed yn seiliedig ar rhwng 10 a 24 ymateb ac wedi'i dosbarthu fel ei bod o ansawdd isel.