You can quite easily check this for yourself: dig up some old school papers, the earlier the better. Then get some old books you have. I expect all of them to still be totally fine.
It depends on the quality of the paper and the ink, almost always it is good and will last a very long time as you said but I've seen cases with low quality paper and low quality ink (pens) that faded away after a year or two.
You say you would type it in a notepad app and then print it. By doing so, there are multiple ways your seed phrase could be stolen. Keyloggers could steal it, or screen capture malware could steal it. Even if you delete the notepad file after you are done,
Technically you should do this on the same computer that the seed phrase was created on. Meaning if the computer is air gap then this risk doesn't exist, if it is not then storing it in a notepad adds only a small risk on top of already very risky setup.
P.S. You don't have to save the notepad on disk to print it.