How often should I wash my hair?

I used to wash it everyday and it would be greasy by the next morning but I've started washing it every third day and it isn't even oily! How far can I push my hair? Will it smell bad? I have really thin hair btw. Thanks!

Cuz I know people in the 70s washed theirs like once a week and it was pretty af but my concern is mostly if it will smell bad