能不能这么说：No matter how old or young we are,it's never too late to learn.

你这完全是中国式英语，old是几岁不是老的意思。你可以这么说：We can learn forever, no matter how old we are.

No matter how old or young we are,it's never too late to learn.
完全正确no matter how old or how young we are中重复了how,可以省略的

No matter how old we are, it's never too late to learn.

我觉得no matter how old or how young we are正确吧

一般要么OLD要么YOUNG，很少2个一起说。
或者你说no matter what the age is