Here's a previous answer to a similar question by /u/svendskov

Here is two archived threads which may help you:

• Is there any documentation of paper airplane-like toys or child playthings prior to the invention/discovery of man-controlled flight?
• In a time before the invention of airplanes, is there any evidence of people making paper airplanes out of paper/parchment?

Furthermore, I remember reading about this article where pre-Wright Brothers paper planes were found during the renovation of St. Anne's Church in Devon, England: Lost ‘squadron’ discovered in old chapel.