Why is paragliding not an old invention? Paraglider looks like a rather simple device for me. It does not have a complex engine that needs lots of technology to be built. It also does not need a powered aircraft just to be launched. Looking from the side I have an impression that it can cover serious distances along the ridge under right wind. While it is not convenient to have the airways bound to mountain ridges, it could still have had uses like patrolling borders or similar.

I am surprised, why the master that could build a bow, or possibly sails for the ship could not build a paraglider many years ago. What are the reasons why the paraglider is relatively recent invention? Is there something complex about is I am not aware of?
Paragliders as we know them depend on parawings with relatively high glide ratios and useful levels of steering.  Neither of these qualities were well represented in the round parachutes (even the so-called glide 'chutes) in common use before modern flat canopy glide parachutes came along (in the 1970s?).  Parawings as we know them were an outgrowth of these highly maneuverable parachutes, modified to have lower loading (for better sink rate) and optimized for horizontal flight, without the need to open in a near-vertical fall at terminal velocity.

If the knowledge had existed, parawings as we know them could have been built as early as the 1860s (when plain, round, uncontrollable silk parachutes came into use for stunt jumps from balloons).  The missing ingredient, as it were, was simply the knowledge that such a thing was useful and possible.