Discrimination is any practice that makes distinctions between individuals or groups to disadvantage some and advantage others. This could be because of attributes such as gender, impairment, religion, race or parental status.
If someone treats you unfairly because of how old you are, it is a form of discrimination. Age discrimination may be unlawful depending on the circumstances.
If you are experiencing discrimination, ask the person to stop what they are doing. Often this will be enough for them to change their behaviour. If talking to them doesn’t work, you may be able to make a complaint to the Queensland Human Rights Commission.