My parks & rec guitar class, the very first night taught us G, D and I think, C chords and had us playing Proud Mary by the time I walked out of that 2 hour class. It didn't sound perfect but I thought it was pretty damn cool.
Hah I was actually trying to make a point that you know enough right this minute to play songs. You just have to find a song that uses the chords you know, or else just learn the god damn G and C chords already! With G C and D you can play literally hundreds of rock songs, including just about Elvis's entire damn catalog.