Title: Marriage in Australia
Content:  The marriageable age for marriage in Australia is 18 years, which is the age of majority in Australia in all states, but in "unusual and exceptional circumstances" a person aged 16 or 17 can marry with parental consent and authorisation by a Magistrates Court. The application to the court must be filed by a parent. For many years, courts have refused to accept a minor's pregnancy as a pressing consideration in deciding whether to allow an early marriage. In addition, the older partner must be over 18. Until 1991, the marriage age was 16 for females and 18 for males, but a female 14 or 15 years (wanting to marry a male aged 18 or above) or a male 16 or 17 years (wanting to marry a female aged 16 or above) could apply to the court for permission to marry. The ages were equalised in 1991, with the relevant ages applying to females being raised to those applying to males.
Title: Marriage in Australia
Content:  Marriage in Australia is regulated by the federal government, which is granted the power to make laws regarding marriage by section 51(xxi) of the constitution. The Marriage Act 1961 applies uniformly throughout Australia (including its external territories) to the exclusion of all state laws on the subject. Australian law recognises only monogamous marriages, being marriages of two people, including same-sex marriages, and does not recognise any other forms of union, including traditional Aboriginal marriages, polygamous marriages or concubinage. The marriage age for marriage in Australia is 18 years, but in "unusual and exceptional circumstances" a person aged 16 or 17 can marry with parental consent and authorisation by a court. A 
Title: Marriage license
Content:  In Australia, there is no requirement to obtain a marriage license. However, a person under the age of 18 requires the authorisation of a judge to marry. Couples must provide their marriage celebrant with a Notice of Intended Marriage at least one month and up to 18 months before a wedding.
Title: Ages of consent in Oceania
Content:  It is an offence in South Australia to engage in any activity which involves fellatio, cunnilingus or placing any part of the body within the labia majora, vagina or anus of a person under the age of 17 unless they are lawful spouses. The Australian Marriage Act can permit someone who is 18 or over to marry a 16-year-old. But, it is a defence if the person is 16 at the time of the offence and either the offender is under 17 years of age or believe on reasonable grounds that the other person is 17 or older. It is also an offence to have sexual intercourse with a person under the age of 18 if that person is under the care of the offender (guardian, teacher etc.).
Title: Marriage in Australia
Content:  documents (apostilles and authentications) and issues Certificates of No Impediment to Marriage (including witnessing the signature on the form). In general, marriages entered into abroad are normally recognised in Australia as valid if they are valid according to the laws of the country in which the marriage took place, except that a marriage is not recognised as valid in Australia if:  So, for example, even though it may be legal for a person under the age of 18 to marry abroad, such a marriage will not be recognised as valid under Australian law, even when the underage partner turns 18. Marriages performed abroad do not require to be registered in Australia, and it is advisable that the couple obtain and retain the marriage certificate from the relevant authority in the country in which the marriage took place.
Title: Marriage in Australia
Content:  Australian law recognises only monogamous marriages, being marriages of two people, including same-sex marriages, and does not recognise any other forms of union, including traditional Aboriginal marriages, polygamous marriages or concubinage. A person who goes through a marriage ceremony in Australia when still legally married to another person, whether under Australian law or a law of another country, commits an offence of bigamy, which is subject to a maximum 5 years imprisonment, and the marriage is void. Since December 2017, Australian law has recognised same-sex marriage in Australia whether entered into in Australia or abroad. The original 1961 Marriage Act did not include a definition 
Title: Australian family law
Content: one or both of the parties were already married at the time (i.e. bigamy) ; the parties are in a prohibited relationship (i.e. closely related such as siblings) ; the parties did not comply with the marriage laws in the jurisdiction where they were married (note that although a marriage contracted abroad is in general considered valid in Australia, in certain cases, such as when there are serious contradictions with the marriage laws of Australia, the marriage is void) ; one or both of the parties were under-age and did not have the necessary approvals, (minimum marriageable age is 16, but 16 and 17 years-olds need special court approval) or ; one or both of the parties were forced into 
Title: Civil ceremony
Content: not be married to someone else ; not be marrying a parent, grandparent, child, grandchild, brother or sister ; be at least 18 years old, unless a court has approved a marriage where one party is aged between 16 and 18 years old ; understand what marriage means and freely consent to marry ; use specific words during the ceremony ; give written notice of their intention to marry to their authorised celebrant, within the required time frame. Civil ceremonies were legalised in Australia in 1973. To be legally married in Australia, a person must: 
Title: Same-sex marriage in Australia
Content:  Same-sex marriage in Australia has been legal since 9 December 2017. Legislation to allow same-sex marriage, the Marriage Amendment (Definition and Religious Freedoms) Act 2017, passed the Australian Parliament on 7 December 2017 and received royal assent from the Governor-General the following day. The law came into effect on 9 December, immediately recognising overseas same-sex marriages. The first same-sex wedding under Australian law was held on 15 December 2017. The passage of the law followed a voluntary postal survey of all Australians, in which 61.6% of respondents supported legalisation of same-sex marriage. Other types of recognition for same-sex couples are also available. Under federal law, same-sex couples can also be recognised as de facto relationships, which provide most of the same rights and responsibilities afforded to married couples, 
Title: Same-sex marriage in Australia
Content:  According to the Australian Bureau of Statistics, approximately 5.2% of all marriages officiated in Australia have been marriages of same-sex couples, since 1 January 2018. Female same-sex couples accounted for the majority of same-sex marriages performed in each state and territory. The 2018 data indicates the overwhelming majority of same-sex weddings are administered by a civil celebrant, and that the median age of same-sex couples entering into marriages is notably older than heterosexual couples. Note that the figures below do not include any marriages where one or both of the parties do not identify as either male or female. Dual British-Australian couples were able to marry in British embassies and consulates in Australia after the United Kingdom legalised same-sex marriage in 2014. From June 2014 to October 2017, 445 same-sex couples took advantage of this and married in British diplomatic offices across Australia.

Question: what is the legal age for marriage in australia?
Answer: 18.