I have a toy train from the 1976 USA bicentennial. I was born in 1974, so it's the oldest thing I've owned since new.

Here's an example on YouTube: https://www.youtube.com/watch?v=4d4e_net1HQ

Made by Lionel to be a 'gotta catch them all' type deal, which they milked for four years if you wanted the full 15 piece set (engine, caboose, and 13 boxcars for the 13 original colonies). I do not have them all, but both my dad & I each had the engine, and between us we had enough of the common cars to build a nice enough playset to run around the Christmas tree.

Mildly interesting, in that Lionel can build some really nice toys, but this was not one of them. Train collectors call this generation the "Mostly Plastic Crap" era, and this set solidly ticks that box. Perhaps interesting (or frustrating), Lionel also made quality stuff during this exact same timeframe. You just had to know what to look for. But in hindsight, probably a good thing this was cheap. If it had been a nice set, I wouldn't have gotten to play with it as a 2 year old...

Over the years I've updated these engines with the better parts, I'd argue they run better than when they were new. Quite proud of that - as a kid I ran my engine until it simply could not run any more. Decades later I was able to not only repair it, but improve it. It will not ever be valuable, but it still makes me happy when I pull them out & run them around. Really triggers the old memories.

Guitar. My dad gave me his 1964 Guild T100D when I was about 15. So I’ve had it for… 40 years!
It’s a beaut. Thin, sunburst hollow body with a pair of humbuckers and beautiful f-holes

I have a coffee cup with Hercules Disney move theme that I drink from daily and is 29 years old.

I have a stuffed animal from my mom’s childhood. I inherited it at some point in mine. Also have some knitted stuffed animals made for me by my great-grandmother when I was a pretty young. As for stuff I purchased myself, I have a pair of combat boots I bought in 1991 or 92 that are still alright. I also have a sweater I bought in college, probably 95 or 96, for $5 on a clearance rack. Thought I lost it last year and was actually pretty bummed.

My stuffed animal that i got when i was born in the hospital shop. Still has sentimental value but is mostly destroyed except the head.

I have a teddy bear that my parents bought for me the day I was born. Made this an easy answer.

My first job 20 years ago I had to buy a chain link replacement because someone drove through the chain we had blocking the entrance to the parking lot. It came in a two pack and I have used the spare on my keychain since then.

My double great grandfather was into coin collecting and I have his coin collection.

That specific coin was the first one he collected out of many niche coins.

I have a playstation 2 memory card somewhere :3, I had that since I was like 4. and yeah I just kinda kept it for the memories.. my mom found it years after our ps2 broke and was gonna toss it but I took it

The original dice from the D&D basic set from the 1980s. The numbers were grooves cut into the die and I had to use a crayon to fill them in so that they'd be more legible. Very sentimental about them.

This hourglass I stole in kindergarten. It was used to measure time for brushing teeth. It also used to have a suction cup, but over the years it partially decomposed.

i migrated when i was 25 with just one suitcase, so easy to narrow down to objects i brought and still have 22 years later, which would be 2 passports, one T-shirt that doesn't fit since long ago, and an altimeter, which i brought because it is small and i used to be into climbing

Bought specifically for me? Super NES and games.

Technically the oldest items are 2 wall clocks I inherited that are from late 1800s, iron skillets that are easily 75-100 years old and a Stanley OG thermos that's from the late 50s.

A copy of Pokemon Yellow I got when I was a little kid. My dad bought a gameboy bag that had a few games in it for like $5 from his coworker. Pokemon was basically my childhood, I loved playing it.

I still have toys family members gave me when I was born.

Probably some of my old SF books. I've definitely had many of them for more than 20 years. There's probably one I've had more than 25 years.

70s alarm clock

My dad created email addresses for me and my siblings when we were born. I still have it, but I wish I didn’t. I’m just way to lazy to switch.

Probably my copy of the book of The Fox and the Hound, that my parents read to me when I was like toddler age. Honestly it doesn't have particular sentimental value other than I think it's cool to still have something from basically when I was born. And it's a lovely story too.

The runners up are probably my two acoustic guitars that are both in disrepair. And a red and blue flannel shirt that has somehow lasted about two decades and never aged or even lost a button.

I have a "marble hornets" shirt from back when they released season 1 on DVD. It's frayed to hell but I still proudly wear it on occasion.

A copy of Junkbots, Bugbots, and Bots on Wheels book I got about 25 years ago. That's when I started my electronics hobby. It's hard to get back to it with the motivation/enjoyment I had before. Holding on to it, maybe the motivation will come back .