To enroll in PhilHealth as a senior citizen, individuals must present proof of age, such as a birth certificate or valid ID showing they are 60 years or older. Additionally, they should provide any necessary documents related to prior PhilHealth memberships, if applicable. Senior citizens can apply at PhilHealth offices or online through their official website. It's also a good idea to check with PhilHealth directly or visit their website for the most current information and any specific requirements that may apply.