Can I just pay old-age insurance and not medical insurance?

You can't.

At present, it is not possible for individuals to pay social security by themselves, but only endowment insurance rather than medical insurance. Individuals need to pay two insurances, medical insurance and endowment insurance. Endowment insurance and medical insurance, the payment period is determined by accumulation.

Legal basis:

People's Republic of China (PRC) social insurance law

Twenty-seventh individuals who participate in the basic medical insurance for employees, when they reach the statutory retirement age, will no longer pay the basic medical insurance premium after retirement and enjoy the basic medical insurance benefits in accordance with state regulations; Those who have not reached the fixed number of years prescribed by the state may pay the fees to the fixed number of years prescribed by the state.

Twenty-eighth medical expenses that meet the basic medical insurance drug list, diagnosis and treatment items, medical service facilities standards and emergency treatment and rescue shall be paid by the basic medical insurance fund in accordance with state regulations.

Twenty-ninth medical expenses of the insured shall be paid by the basic medical insurance fund, and shall be directly settled by the social insurance agency, medical institutions and pharmaceutical business units.

The administrative department of social insurance and the administrative department of health shall establish a settlement system for medical expenses in different places to facilitate the insured to enjoy the basic medical insurance benefits.