when + 名词 （省略）

请教下面两句状语从句+名词短语省略是否是错句：

He was fond of painting when yet a child. (=when he was yet a child)

Although the youngester of the class (=Although he was the youngest of the class), Nigel came out first in the end-of-term examination.

语法上是不错的，分句中主谓与主句主的主谓一致就可以省略