Is there anything that you regret not doing in your teen years that have impacted your career?

As soon as you can, get involved with the types of activities that you care about and where your skills and talents are used. The sooner you begin to gain experience and make connections with other people, the more you expand your world and the more options you have.

Without a doubt, travel internationally.

There are missed opportunities, both in teen and adult years.
1. There was a class in college, called "moot court," that was only available to those who were invited by the professor to take it. It is a high level law class, where the class is divided into two teams. They spend the semester researching one topic, then at the end of the semester, one side argues "for" and the other "against," like in a trial. Although my professor invited me to participate, I did not have the self-confidence, and turned it down.
2. College internship: it was volunteer, working for an investigative reporter. I totally messed up the first assignment he gave me, then convinced myself that I should not be doing the internship because he was just using me to run errands, and I had to pay my own parking. So I quit. He was an award winning reporter, and the story I would have been working on was one of the top stories of the year.
3. In the police academy, one of the instructors offered to get me a position with an insurance company as an insurance fraud investigator. I did not want to leave law enforcement, so I declined. It would have been a much better career path than law enforcement, at least for me.

One that I do not regret: I was given the opportunity to run the Training Section at the Police Dept. There were many things wrong with how that Section had been run in the past, and I was able to see changes that needed to be implemented. When they offered me the position, I asked about having the room to change certain things, and they said NO. It was very much "micro-managed." So, knowing I would not have the latitude to actually "run" the Section, I said no.

As for "Teen" years, I regret taking only the minimum amount of science in high school. I was afraid of chemistry and physics. Originally I wanted to go into microbiology, but I let the difficult subjects scare me away. And, I regret not partying/hanging out with fellow teens. I somehow thought that only "bad" kids did those things.

While there are many professionals now days who try to plan their entire career, the truth is, along the way, unexpected opportunities present themselves. If you do not at least seriously consider them, you may later have regrets.