The Tripods (TV series 1984-1985)

Earth has been conquered by an alien race known as the Masters using their giant Tripods. When humans reach the age of sixteen, they must undergo a process known as capping which places their mind under the control of the conquerors. In 2089, having learned the truth, cousins Will and Henry Parker embark on a journey to the White Mountains in search of a group of free men. - IMDb