The minimum legal age for marriage in Hong Kong is 16 years of age (Gregorian reckoning). You can choose to register for marriage in Hong Kong regardless of where you live or what your nationality is.
The following website provides information on marriage registration, including giving the notice of intended marriage on the prescribed form in Hong Kong or from places outside Hong Kong, celebrating your marriage in different venues as well as post-registration of marriage taken place before 7 October 1971:
GovHK - Marriage Registration
If you plan to get married with your partner in the Mainland, you have to go through marriage registration procedures in accordance with Mainland laws and regulations. Marriage registration in the Mainland is the duty of the home affairs offices of the governments of provinces, autonomous regions and municipalities, or the authorities designated by the home affairs offices.
You may refer to the website of the Shanghai Civil Affairs Bureau for a guide to marriage registration for Shanghai and Hong Kong residents, policy papers and information about the institutions responsible for the registration. For information on the required procedures and documents for marriage registration by governments of other provinces, autonomous regions and municipalities, please contact the relevant marriage registration authorities.
Under the Laws of Hong Kong, you will have to go through the following procedures to solemnize a marriage in Hong Kong:
Either one of you has to give a Notice of Intended Marriage (the notice) to the Registrar of Marriages (the Registrar) in the prescribed form either directly or through a civil celebrant of marriages.
The Registrar shall exhibit the relevant part of the notice in his office until the issue of a Certificate of Registrar of Marriages or the expiry of the 3-month period.
The Registrar may, at least 15 days after the giving of a notice, issue a Certificate of Registrar of Marriages to enable you to celebrate your marriage within three months from the date of notice giving if all the statutory requirements are met.
A marriage has to take place at a marriage registry by a Registrar; or in a licensed place of worship by a competent minister or at any other place in Hong Kong by a civil celebrant of marriages.
If the marriage does not take place within three months after the giving of the notice, the notice and all proceedings thereupon shall be void. You have to give another notice before getting married.
For information on the registration of a marriage, please click on the following link:
https://www.immd.gov.hk/eng/marriage/Registration_of_a_Marriage.html
A certificate of absence of marriage record is a document certifying that a person has not registered any marriage in Hong Kong. You may submit your application for a certificate of absence of marriage record to the Hong Kong Immigration Department by post, online, in person or through an authorised representative.
If you apply by post and the result shows that you have no marriage record in Hong Kong, you will be notified by post of paying the fee(s) required for obtaining a certificate of absence of marriage record. The certificate will be posted to you at the mailing address indicated in the application form on receipt of the required fee(s). If the search result shows that you have a marriage record in Hong Kong, a letter of marriage record will be posted to you.
If you apply online, in person or through an authorised representative, you have to collect the certificate of absence of marriage record or the letter of marriage record in person or through an authorised representative at the Marriage Registry of the Immigration Department in Hong Kong.
For information on the application for a certificate of absence of marriage record, please click on the following link:
https://www.immd.gov.hk/eng/services/marriage/Certificate_of_Absence_of_Marriage_records.html