My oldest system in terms of how long I've owned it, and also pretty close to being my the oldest overall, is my Intellivision.
When I was around 5 or 6 and started getting into video games (they had an SNES and Genesis at my daycare) I really wanted one of my own, but convincing your parents to buy such a thing is not always an easy task. I told my dad and he went into his closet and pulled out the Intellivision. To this day I can't get over how odd that is, because my dad never played any kind of video games in my lifetime. He gave it to me and my brother as well as the 5 or so games he had for it.
Over time he would pick up random games from the flea market he went to weekly (One that had been going on for decades as a community tradition that got closed down in the late 2000s when the land changed hands, to be developed into nothing yet still a decade later...) and give them to us, so we built a decent collection. The unusual nature of the system that no one I ever met in school knew of really kickstarted my interest in collecting video games.
It was technically in my family even before I was born but I've personally owned it for about 25 years, about 80% of my total lifetime.
