When did the youngest US Open men's singles champion in history retire?
2002
2018
2016
2021
2018
2016
2018
2021
2017
2016
2018
2008
2021
2014
2017
2016
2018
2008
2015
2014
2017
2009
2016
2021
2018
2008
2015
2014
2017
2009
2016
2018
2008
2015
2021
2013
2012
2014
2004
2017
2009
2016
2010
2018
2008
2015
2013
2012
2005
2021
2007
2014
2004
2017
2009
2016
2010
2006
1999
2018
2008
2001
2015
2013
2002
2003
2012
2005
2007
2014
2004
2017
2009
2016
2021
2010
2006
2000
1999
2018
2008
2001
2011
2015
2013
2002
2003
2012
2005
2007
2014
2004
2017
2009
2016
1998
2010
2006
1990
2000
1999
2018
2008
2001
2011
2015
2021
2013
2002
2003
2023
2012
2005
2007
2014
2004
1996
2017
2009
2016
1998
2010
2006
1990
2000
1999
2018
2008
2001
2011
2015
2013
2002
1993
2003
1988
2012
2005
2021
2007
2014
2004
1996
2017
2009
2023
2016
1998
2022
2010
2006
1990
2000
1999
2018
2008
2001
2011
2015
2013
1991
1989
2002
1993
2003
1988
2012
1995
2005
2007
2014
2004
1994
1996
2017
2009
2016
1998
2019
2010
2006
1990
2000
1999
2018
2023
2008
2001
2011
2015
2022
2013
1991
1989
2002
1997
1993
2003
1988
2012
1995