From the article:

"In adolescence, the brain is also buzzing with more dopamine activity than at any other time in the human life cycle, so everything an adolescent does—everything an adolescent feels—is just a little bit more intense. “And you never get back to that intensity,” says Casey."

I agree with this.

I feel much less alive now than when I was an adolescent.

And you really do never get that feeling of "aliveness" back, for lack of a better word.