OK, so we know that many of the force powers used by the Jedi of Old have been lost due to the Imperial policy of Jedicide *:o)
In the movies and books we are only exposed to a handful of the Jedi that survived and were able to make HoloVision headlines.
Source: wiktionary
I wonder how long before Luke was born did the Jedicide begin. I'm guessing about 30 years before ANH, because I believe Anakin was about 25 when that all happened, since Vader was 50 in ESB (according to my ESB trading cards).
Source: wiktionary
> Also, Obi-Wan tells Luke that Vader helped the Emporer^([sic]) hunt down and kill the Jedi Knights.
[…]
But we only have Obi-Wan's word about the Jedicide. And we know how trustworthy *that* is!
Source: wiktionary