I have come across several pieces of spacecraft debris on ambergris caye over the years. The largest was the size of 3 queen size beds and I was able to decipher the owner.... Arienspace
Arienspace is a French lead consortium and has a launch site at French Gayana. The components found on the beach are often parts that are jettisoned on purpose, like the clamshell doors that protect the cargo, usually telecommunications satellites, during the launch and early assent stage.
Once into the thinner air at altitude they are discarded as trash into the ocean, just like Coke, Pepsi and Snapple group containers!
I wrote the boards of these four companies pointing out they're responsibility for their share of the beach trash blight on ambergris caye. Not surprisingly I never received a response.
All this to say, don't assume the space trash is old. It's likely only as old as the time it took to drift ashore unhindered.