The JJ Cooper article around the time that he defected debunked the 26 claim:

But nothing seems to have stuck more than Jack Curry’s report in the New York Times that Aroldis Chapman may be 26 years old, five years older than the 21 he’s listed at by the Cubans. That story said that “reports in March at the World Baseball Classic said he was 26.”

That age is based on a New York Times story from the World Baseball Classic on March 13, when Dan Rosenheck listed Chapman’s age as 26. That report was erroneous. When reporting for our Top 10 Prospects from the World Baseball Classic Premium, all of the scouts we talked to said they believed Chapman was 21.

A quick Google Search of “Aroldis Chapman actually 26” shows that the Times report has quickly become the accepted standard, raising significant questions about Chapman’s age. But in addition to not have any real documentation behind it, the report also doesn’t pass the logic test. Why would Cuba lie about a player’s age? Cuba doesn’t want to see its players defect. Lying about Chapman’s age to make him seem younger could have a minor benefit in giving Cuba a better chance win the occasional age-group international tournament (although Chapman has been playing on the senior national team), but it would also raise the likelihood that Chapman would defect for riches in the U.S. If the Cuban government had incentive to mislead, it would want to make its players appear to be older than they are–a 35-year-old pitcher isn’t as likely to land a multimillion dollar deal in the U.S. as a 25-year-old.

Some Cuban players’ ages have been misstated in the past–largely by agents and others trying to get the players big paydays after they have defected. But in Chapman’s case, there is documentation that he’s 21 (and will turn 22 in September), and no credible documentation of anything else. International scouts have been keeping an eye on him every since he broke into Cuba’s Serie Nacional late in 2005 as an 18-year-old. He made his first appearance for Cuba’s national team at the Pan American Games 2007 as a 19-year-old. If he was 26, there would have been no reason for Cuba to have kept him under wraps for several years when he could have been helping the team in the World Baseball Classic and other national tournaments.[/quote]
http://www.baseballamerica.com/blog/draft/?p=1303

There is no reason to raise concerns about his age. I’m much more confident in Chapman being 22 (I didn’t realize that his birthday was in September in the previous post) than I am about any other international signee’s age being accurate.

The JJ Cooper article around the time that he defected debunked the 26 claim:

Chapman set off a flood of speculation when he defected from the Cuban National team last week, with questions about whether he’ll break the international signing bonus record, when he will become eligible to sign and which club will end up landing him.

But nothing seems to have stuck more than Jack Curry’s report in the New York Times that Aroldis Chapman may be 26 years old, five years older than the 21 he’s listed at by the Cubans. That story said that "reports in March at the World Baseball Classic said he was 26."

That age is based on a New York Times story from the World Baseball Classic on March 13, when Dan Rosenheck listed Chapman’s age as 26. That report was erroneous. When reporting for our Top 10 Prospects from the World Baseball Classic Premium, all of the scouts we talked to said they believed Chapman was 21.

A quick Google Search of "Aroldis Chapman actually 26" shows that the Times report has quickly become the accepted standard, raising significant questions about Chapman’s age. But in addition to not have any real documentation behind it, the report also doesn’t pass the logic test. Why would Cuba lie about a player’s age? Cuba doesn’t want to see its players defect. Lying about Chapman’s age to make him seem younger could have a minor benefit in giving Cuba a better chance win the occasional age-group international tournament (although Chapman has been playing on the senior national team), but it would also raise the likelihood that Chapman would defect for riches in the U.S. If the Cuban government had incentive to mislead, it would want to make its players appear to be older than they are–a 35-year-old pitcher isn’t as likely to land a multimillion dollar deal in the U.S. as a 25-year-old.

Some Cuban players’ ages have been misstated in the past–largely by agents and others trying to get the players big paydays after they have defected. But in Chapman’s case, there is documentation that he’s 21 (and will turn 22 in September), and no credible documentation of anything else. International scouts have been keeping an eye on him every since he broke into Cuba’s Serie Nacional late in 2005 as an 18-year-old. He made his first appearance for Cuba’s national team at the Pan American Games 2007 as a 19-year-old. If he was 26, there would have been no reason for Cuba to have kept him under wraps for several years when he could have been helping the team in the World Baseball Classic and other national tournaments.

http://www.baseballamerica.com/blog/draft/?p=1303

There is no reason to raise concerns about his age. I’m much more confident in Chapman being 22 (I didn’t realize that his birthday was in September in the previous post) than I am about any other international signee’s age being accurate.