I keep everything forever. But only as pdf files on a remote hard drive.
You people need to move more. I have big shredding parties every time I move (6 times since 2004)
I’d rather keep tax records forever than move 
I have the actual returns since I started filing. All backup documentation (farm, rental, business income & expenses) gets shredded at 7 years. As mentioned previously, any property records or something affecting basis is kept.
I use the same rules for keeping client records. If you think personal paperwork can get overwhelming, try doing it for several hundred clients. One firm where I was previously employed had paper copies of returns going back to 1930 for one client. We spend an entire summer microfilming and shredding.