DORTMUND, Germany — There are times these days when Marco Reus finds himself in the middle of the field at Borussia Dortmund’s Signal Iduna Park, watching as Jadon Sancho and Jacob Bruun Larsen and Achraf Hakimi tear around him, a blur of yellow and black, and remembering what it was like to be young.

Not that Reus is what most of us would call old; he is not quite what his peers would call old, either. That is how he feels, though. “I am old, my friend,” he said. “In our business, now, when you are 29 or 30, you are old.” He delivers it with a smile, an acknowledgment that he is hamming it up, just a little, but the sentiment is real.

Reus feels old in the sense that he is starkly aware that he is no longer young. He knows that whenever he sees Sancho, Larsen and the rest of Dortmund’s shooting stars, the way they play with boldness and fearlessness. They look to him like “young horses,” wild and free.

Reus knows that feeling well, that glorious weightlessness, unencumbered by thoughts of “what will happen later, what happens after you finish,” the end so distant that you cannot believe it will ever come.