Has Warren Buffett gotten too big or too old?

Insider Monkey runs an analysis, and finds:

Contrary to the general perception, Buffett has not had any alpha for the past 10 years. Let us repeat that: Buffett, no alpha, for the past decade. You would have been better off if you had invested your money with David Einhorn. Warren Buffett had a phenomenal annual alpha of 19% between 1956 and 1968. Our current analysis shows that his alpha was more than 30% between 1977 and 1981. During the 80′s and 90′s, his annual alpha declined but was still better than 12%. For the ten years leading to mid-2003, his annual alpha stayed around 12% per year. Since then, it started a steep decline; by the end of 2004 it was (still a respectable) 6% per year. Between 2005 and 2008 Buffett’s alpha averaged only 3% per year. Finally, in the ten years ending in 2009, it went virtually to zero.

Whether in sports or Nobel prizes in science, it seems a person's greatest achievements tend to occur in their twenties and thirties. But I think at least part of the decline here can be found in Berkshire's $200 billion market cap. It's a lot harder to move in and out of opportunities when you are piloting a supertanker versus a speedboat.