Not a particularly _safe_ example, but Venezuela recently released 100 year treasury bonds. I'd imagine this is not a retail investment vehicle; traditionally.
If they pay a coupon every year, and you can resell them on a market at any time, then the fact that they won't mature for a hundred years doesn't make them unsuitable for ordinary investors.
Now, a hundred year term deposit, with interest payable at maturity ...
Argentina is not particularly a glowing example of an entity with such a long investment horizon given how frequently they've defaulted on their debt.