Max validity of Schengen visas is 5 years and that too is restricted only to countries with treaty agreements for this (eg. Russia).

For Indians, 2 years is the current maximum permitted. I've received 2 year Schengen visas consecutively from the Dutch, French, Germans and Dutch again in various parts of the world over the last few years.

Never had to show any invitation from a European partner (just a covering letter from myself), but I have over 200 visits to 18 different Schengen countries during this period so I guess I'm considered low risk as a result.