Arizona Cardinals Kurt Warner performed excellently in their recent 51-45 victory over the Green Bay Packers, tossing more TD's (5) then incompletions (4). His announcement that his next loss will be his last, as he is retiring after this season, has pundits debating his legacy.
While he has had some truly astounding years, he didn't start until he was 27 and had a long stretch of mediocrity.
http://www.stltoday.com/blogzone/round-two/round-two/2010/01/kurt-warners-amazing-run/