Adam Committed Capital Murder When He Was 16 Years Old

Adam committed capital murder when he was 16 years old.Under Texas state law,when can he legally be transferred to an adult prison?

A) Immediately upon conviction
B) When he reaches age 19
C) After he has served 10 years in a juvenile facility
D) If he commits another crime while an inmate in a juvenile facility
E) Never,because the offense occurred when he was a juvenile