All ballplayers share one statistic. Each year, they are a year older.

Another statistic: According to 2010 U.S. census data, more people graduate from college in Boston than any other metro area in the United States. During and after college, many of these kids play baseball in local amateur leagues. And 10 years after that, these guys are ready for the senior leagues. Therefore, it’s not surprising that senior leagues in Boston have seen explosive growth in recent years. One of the key men behind this growth is Paul Harrington.

Today, Harrington lives in South Grafton, Mass., where he moved two years ago. Before that, he spent the previous 53 years of his life living smack in the middle of Boston. Harrington was never blessed with the skills to play high school or college ball, but he always had the bug to play.

In 1977, Harrington started a team in the Boston City League. As its name suggested, the City League was run by the City of Boston, and consisted of loosely organized games as a recreational activity. Years later, the league transitioned to the Boston Twi-League, also run by the city. Eventually, the Twi-League broke off from the city and became the Boston Junior Park League — the “minor league” counterpart of the still prominent Boston Park League.

Today, the Boston Junior Park League has grown into the Yawkey League, one of the city’s prominent amateur leagues.

Harrington moved along to other baseball circles about 1988. It was then that the Boston Men’s Senior Baseball League (MSBL) was formed. Paul added a team to their Age 30+ division, and ultimately became vice president of the league.

In 2003, Harrington started his own league, the Boston Amateur Baseball League (BABL). He continues to serve as president of that league today, also managing a team in each of his three age divisions.

Paul heads the Metro Blue Jays in the Age 38+ division, the Montgomery Blue Jays in the Age 48+ division, and the Mudville Nine in the Age 55+ division — a new division that was just added last season, and as far as he is aware, the oldest age division league in New England.

The age splits may seem peculiar. There are several 30+ or 40+ leagues, but 38+ and 48+ seems like odd age breaks. I asked Paul about this.

“We went with slightly younger ages than we wanted to attract more players,” Harrington said. “Each time a league comes along for an older group, people are hesitant to embrace it be old. So the league takes some time to grow. Going with 38+ mostly attracts those aged 40 or older, but allows them to feel a little younger and be more accepting of playing in the league.”

The BABL began with 11 teams a decade ago. In 2013, Harrington expects double that count, fielding 22 teams.

“When I was really young, you played baseball into your 20s, then retired to play softball. Now, a 38-year-old guy can be a rookie again in a senior league. Those younger guys all make it to the older leagues eventually. A lot of those guys continue to play in the younger leagues, too, so they are playing in both leagues. There is a lot of baseball being played.”

If players old enough to play in senior leagues had the talent to play in the premier leagues, why would they played senior league at all?

“It’s hard for guys who are 40 to play with guys who are 18. Even if they can keep up ability-wise, there is something different going on with the cultural exchange,” Harrington said.

“Being older, my perspective on life is different. The language, the slang, the technology. It’s all vastly different. By playing with people more my own age, I can have conversations where we don’t leave anybody feeling left out.”

As players age, they actually gain more flexibility to play baseball.

“As younger guys get older, they have children, and their kids become important, and they have less of a commitment to an adult baseball league. After their kids get older and don’t want Dad around as much, these guys have more time to play baseball again. I especially see this see in the 48+ league. They have more time because other things that once kept them busy are not as crucial. Their kids don’t need them. They don’t need to push as hard at work for the next promotion. They can focus more on baseball. They have more time. And they want to play again.”

Contrary to one what might think, Harrington doesn’t believe that getting older impacts the competition level either.

“Baseball is baseball, no matter what level you’re playing at. As long as both teams are equal, you have the same competition level. Off the field, it might be different. But on the field, everybody plays to win. Players actually tend to work better with their teammates when they get older. They have more of a mature attitude. Once you get between the lines, it’s still a bunch of old guys playing a kids game.”

It’s easy to understand why at age 55, Paul added a 55+ league last season. But when does it stop. 60+? 70+? 80+?

“As long as the demand is there, we’ll get older and keep playing baseball.”