They are old.They weren't old then.They were young.

他们很老。那时他们不老。

(那时)他们很年轻。

She is tall.She wasn't tall then.She was short.

她很高。那时她不高。(那时)她很矮。

It is clean.It wasn't clean then.It was dirty.

它很干净。那时它不干净。(那时)它很脏。