The title of this movie is The Irishman

Rating: 1/10 (1 November 2019)

Can someone please explain to me why a 76 year old, 5'-10", Italian American (De Niro) is play a 42 year old, 6'-4", Irish guy (Sheeran)? Especially when the name of the movie is called The Irishman. Almost as bad as casting Tom Cruise as Jack Reacher.