Depends.
Oldest thing that was originally mine?
A little plastic horse. There is a picture of me aged < one year lying on the dining room table looking at it. I can reach out from here and take it down from a shelf. I’m 54.
Oldest thing that has been in the immediate family that I have close at hand? My grandfather’s, then my dad’s Mossberg 151 .22. I learned to shoot with it at 8 years; it had to be supported by a pillow at the front.
Oldest thing that has been in the extended family?
1908 Pathe cabinet phonograph.
No slide rules, and the oldest calculator is from the 1990 and would be found risible by an engineer.
Now that you pointed out a gun I just realized. Above me on the wall is a 30-40 Krag from the early 40s. It also has been passed on down. I also have a picture of me holding it in ‘55 or ‘56. Yes did some shooting with it but never killed or shot at a deer.