Per default, set current date for newly created page - how?

From time to time i real an old blog post it wrote and when i discover a type i update the post. The problem here is that per default this saves the current date and the post is on top, which i don’t want.

I can of course set the date manually but how would i do that automatically? I would like, at the time a post is published, to set the current date & time, so that the next time i change a post that date will stay and i don’t have to set that manually to keep the date.