How long woud a lenovo all in one PC live for?

It won't just burn out or something… Most pc's work for at least 5 years but since this is a pre build pc you won't be able to upgrade sadly.

There's no way to tell. I'm sure that there are computers from nearly 30 years ago that are still working just like the day they were first bought. We have a nearly 7 year old system that still works fine.

Just give your computer regular maintenance and you should be fine. Usually, just opening the case every other month and cleaning the dust off should adequate.