Fancasting Dick and potentially Tim and Jason for this feels like a bit of a hopeless proposition due to the likelihood of it being complete unknowns being quite high and the fact that at least for Dick the age range could really be anywhere from 18-30 right now as we aren't sure how old Batman will be, but here's a list of young actors that could be in contention anyway (some data could be wrong as admittedly I aided myself with using Bing Chat for the info on ages and heights since it was too much of a hassle to individually search for it)
Aidan Gallagher: September 18, 2003 (20 years old) - will be 22-23 years old when filming. Height: 5’5"
Gabriel LaBelle: September 20, 2002 (21 years old) - will be 23-24 years old when filming. Height: 5’9"
Milo Manheim: March 6, 2001 (22 years old) - will be 24-25 years old when filming. Height: 6’2"
Tom Taylor: July 16, 2001 (22 years old) - will be 24-25 years old when filming. Height: 5’7"
K.J Apa: June 17, 1997 (26 years old) - will be 28-29 years old when filming. Height: 5’11".
Alex Wolff: November 1, 1997 (25 years old) - will be 28-29 years old when filming. Height: 5’11"
Tanner Buchanan: December 8, 1998 (25 years old) - will be 28-29 years old when filming. Height: 6’0"
Owen Teague: December 8, 1998 (25 years old) - will be 28-29 years old when filming. Height: 6’0"
Matt Cornett: October 6, 1998 (25 years old) - will be 27-28 years old when filming. Height: 6’0"
Colyn Mylchreest: May 8, 1998 (25 years old) - will be 27-28 years old when filming. Height: 6’0"
Zachary Gordon: February 15, 1998 (25 years old) - will be 27-28 years old when filming. Height: 5’9"
Tye Sheridan: November 11, 1996 (25 years old) - will be 27-28 years old when filming. Height: 5’7"
Dylan Minnette: December 29, 1996 (27 years old) - will be 29-30 years old when filming. Height: 5’9"
Lucas Hedges: December 12, 1996 (27 years old) - will be 29-30 years old when filming. Height: 5’11"
Harris Dickinson: June 24, 1996 (27 years old) - will be 29-30 years old when filming. Height: 6’0"
Austin Abrams: September 2, 1996 (27 years old) - will be 29-30 years old when filming. Height: 6’0" .
Thomas Doherty: April 21, 1995 (27 years old) - will be 29-30 years old when filming. Height: 6’0" .
Nick Robinson: March 22, 1995 (27 years old) - will be 29-30 years old when filming. Height: 6’2" .
Taz Skylar: December 5, 1995 (27 years old) - will be 29-30 years old when filming. Height: 6’0" .
Isaac Cole Powell: December 30, 1994 (27 years old) - will be 29-30 years old when filming. Height: 6’2" .
Tom Blyth: February 2, 1995 (28 years old) - will be 30-31 years old when filming. 6'0
Dónal Finn: August 31, 1995 (28 years old) - will be 30-31 years old when filming.
Jonah Hauer King: May 30, 1995 (28 years old) - will be 30-31 years old when filming. Height: 6’0"
Hero Fiennes Tiffin: November 6, 1997 (26 years old) - will be 28-29 years old when filming. Height: 6’2"
Fionn Whitehead: July 18, 1997 (26 years old) - will be 28-29 years old when filming. Height: 5’9"
Jacob Elordi: June 26, 1997 (26 years old) - will be 28-29 years old when filming. Height: 6’4"
Ewan Mitchell: March 8, 1997 (26 years old) - will be 28-29 years old when filming. 5'10
Alex Hogh Andersen: May 20, 1994 (29 years old) - will be 31-32 years old when filming. 5'11
Nicholas Galitzine: September 29, 1994 (29 years old) - will be 31-32 years old when filming. 6'0
Dacre Montgomery: November 22, 1994 (29 years old) - will be 31-32 years old when filming. Height: 5’10"
Charlie Heaton: February 6, 1994 (29 years old) - will be 31-32 years old when filming. Height: 5’10"