引导的让步状语从句必须倒装;though引导的让步状语从句可以倒装也可以不倒装;而although引导的让步状语从句不能

as引导的让步状语从句必须倒装;though引导的让步状语从句可以倒装也可以不倒装;而although引导的让步状语从句不能倒装. 这句话对吗?
这句话对的.
例如：As young he is, the boy really knows a lot.
Though young he is, the boy really knows a lot.
Though he is young, the boy really knows a lot.
Although he is young, the boy really knows a lot.