The offence of unlawful carnal knowledge is contained in section 215 of the Queensland Criminal Code. In colloquial terms, the offences refers to any act of or attempt at sexual intercourse with a person under the age of 16 years. The age of consent in Queensland is 16 years. Unlike other jurisdictions, Queensland does not have so called "Romeo and Juliette" laws.
The maximum penalty is life imprisonment if the complainant was under 12 years of age. Otherwise the maximum penalty is 14 years imprisonment.
In some cases, the charge of unlawful carnal knowledge may be finalised in the Magistrates Court. Where the accused is pleading not guilty, or where a circumstance of aggravation applies, the applicable jurisdiction is the District Court of Queensland.
It is a defence to the charge if the accused person can show that they believed, honestly and reasonably, that the complainant was 16 years or over. You can read more about the "mistake of fact" defence and Queensland consent law here and here.
As with other types of sexual offences, being charged with unlawful carnal knowledge is a serious matter. It is not uncommon for sentences of imprisonment to be imposed, including with actual custody. Other consequences may include not being able to apply for a blue card, having a recorded conviction, and being a reportable sex offender under the Child Protection (Offender Reporting) legislation.