You don't want to say: " you're a fuddy duddy" .

“你是个老顽固。”

Mr Smith he's such an old fuddy duddy I can't stand any of his history classes.

史生是个老顽固，我无法忍受上他的历史课。

If indeed I still sound like a lecturer, and somewhat of an old fuddy- duddy, it is because old rock head Ruburt continues in his own ways, as is to be expected.

我听起来确实还像个讲师，有点像个老古板，那是因为老顽石鲁伯还在继续我行我素，这是意料中的。