I'm no expert, but it looks shaky to me. He would have been in his 80s at the time. But it looks slowly drawn.
That said, my son pulled a Stan Musual autograph card last year that looks like a child's attempt at a forgery. The last year or two of his life Musual's signature became almost illegible. Maybe somebody here is more familiar with Cy Young. Personally I'd be careful with the Young autograph unless some very experienced people gave it a thumbs up.