N.H. Rev. Stat. Ann. § 621:9-a

Notwithstanding any provision of law to the contrary, a minor over whom the court has exercised jurisdiction pursuant to RSA 169-B:4, I or retained jurisdiction pursuant to RSA 169-B:4, V(c), may be committed or continue to be committed at the center pursuant to RSA 169-B:19, I(j) until the minor's eighteenth birthday.