This is already addressed in the article, e.g. here:

    There might, however, be a dark side to the story. There is
    a good reason we were designed to have finite sensitive
    periods. Takao Hensch, a Harvard neuroscientist, has
    written that plasticity takes a lot of energy: It’s
    exhausting to keep all your neural circuits in a dynamic
    state. Restricting it may protect the brain.

and in the paragraphs thereafter (I don't want to quote them here in full).