Superman debuted in
Action Comics #1 in
1938.
The Silver Age (aka "Earth-1") version came about sometime in the late 50s/early 60s; there was no hard reboot, but for the sake of this argument let's say it was
1960, when he appeared alongside other silver age heroes in the first appearance of the Justice League of America.
The Post-Crisis (aka the "Byrne") version debuted in
Man of Steel #1 in
1986.
And now the DCnU reboot will come out in
2011.
22 years between the debut and the silver age version
26 years between the silver age and Post-Crisis versions
25 years between the Post-Crisis and the DCnU versions
Looks like we're right on schedule!
Expect a brand new reboot of Superman for his 100th Anniversary in 2038...
