Section 4T. A health maintenance contract, except certificates which provide stand-alone dental services, supplemental coverage to Medicare or other governmental programs, shall provide, as benefits to all individuals or to group members having a principal place of employment within the commonwealth, coverage to eligible dependents under 26 years of age or without regard to age, so long as the dependent, who is covered under the membership of the dependent’s parent as a member of a family group, is mentally or physically incapable of earning their own living due to disability.