Phillippe and Witherspoon, 38, went their separate ways after eight years of marriage amid rumours that the actor had cheated with Australian actress Abby Cornish.
He opened about the split during a recent appearance on Larry King Now. The "Secrets and Lies" actor kept details of their unraveling marriage close to the vest, but did pinpoint one reason it did not work out.
"I think more of the problem was age. When we got together we were so young," Phillippe, 40, who met the "Wild" actress on her 21st birthday, said.
Phillippe said that the exes are "very much" still friends, and have remained amicable while raising their daughter Ava, 15, and son Deacon, 11.
The Crash star has been dating civil rights lawyer Paulina Slagter for the last four years.
After a two-year romance with Jake Gyllenhaal, Witherspoon married CAA agent Jim Toth in March 2011. They welcomed two-year-old son Tennessee, the following year.
