Sorry, I have a stupid question. I was doing some research and I read something that said Linux was based on a 30-year old operating system. Is it true?

You could say that it is based on Unix. So it is based on a 30 year old OS.

To tell you the truth, I'm glad its based off a older OS as you have to realize, older things are more stable than newer stuff that have or going thru testing to see how they withstand current technology.

Older technology that still exists and just being added on to with new development would seem to be more liable/stable than say, something that was developed a year ago and only a % have used compared to the technology that's been around longer than some have been alive working on it now..

But remember though, its based off of Unix but its not Unix.

My car is based off of a 130 year old engine design.
My T.V. is based off of a 80 year old cathode ray tube design.
My Radio is based off of a 60 year old transistor design.
My vaccume cleaner design has been around for 70 years.
The plane I flew last month had jet engines based off of a design from the 1930's.

If it ain't broke, don't fix it.

slight