Another way to read the original post's "due to age" might be the age of the content itself, rather than the age of the user downloading it.
For example, you can't get a digital copy of the original Star Wars theatrical release, but there are fan conversions of old VHS or film reels and additional reconstructions that aren't legally available, but are certainly out there. I know that when I was doing pop-culture research for a thesis on pre-WWII American Cartoons I ran into a lot of works that were only digitized by amateurs and hobbyists, and therefore not legally available anywhere.
Good point. I guess both are reasons people are blocked, and the age of content is one that does apply to OP's point.
But now that I've thought upon it, I do wonder how people feel about the age of viewer issue, especially since people can easily lie about their age or otherwise pirate the content.
For example, you can't get a digital copy of the original Star Wars theatrical release, but there are fan conversions of old VHS or film reels and additional reconstructions that aren't legally available, but are certainly out there. I know that when I was doing pop-culture research for a thesis on pre-WWII American Cartoons I ran into a lot of works that were only digitized by amateurs and hobbyists, and therefore not legally available anywhere.