How old was jasper hale when he got turned into a vampire?

Jasper Hale is the mate of Alice Cullen in Twilight. He has the ability to control people's emotions and feel them/know them. He was in Texas during one of the war's and three girls found him. They were vampires. They needed someone like him to help them, so they changed him. Then, he and Alice found one another and together they found the Cullens.