All persons with legal capacity can sue and be sued. Legal capacity refers to the right or ability under the law to be able to engage in a particular undertaking. Legal capacity is generally determined by age and mental status. Therefore a person intending to sue should be an adult (18 years and above); and of sound mind. The law may also prescribe other circumstances under which a person may sue.
Nevertheless, this does not bar a minor (someone below 18 years), or an insane person from suing. A minor/insane person can sue through a Next Friend. This is a person appointed by Court to represent another who is under disability or otherwise unable to maintain a suit on his or her own behalf.
A person according to the law may be a natural person or a legal person e.g. a company.
Before rushing to sue, make sure you have capacity to sue.