The first time I thought it, a few decades ago[HS or college], I thought it was original. I just Googled it, and the earliest attribution I found was to John Keats. (Interestingly enough, this thread has made it to the second page of the results). The quote seems to have its own Facebook page.

The quote having it's own Facebook page is probably because of the changes they made fairly recently with people's profiles/interests.

I think the quote, an unlived life is not worth examining, is nice and deep. I take it to mean that, not just a boring life, biographies of young people are premature.

As an example, the 24 year old who chases a small bag of air around a grassy field, has a 5-book biography planned.[1]

The man who created the Red Army, lost the struggle against Stalin, inspired revolutionaries around the world and was brutally murdered aged 60... He managed a measly 3 part biography.[2][3]

[1] http://news.bbc.co.uk/sport1/hi/football/teams/m/man_utd/478... [2] http://www.google.co.uk/search?q=inauthor:%22Isaac+Deutscher... [3] http://www.lrb.co.uk/v26/n23/neal-ascherson/victory-in-defea...