Under what condition is a mistake of age defense available?

The mistake of age defense in Canadian criminal law primarily applies in situations involving sexual activity with a minor, specifically in relation to the definition of consent under the Criminal Code. The defense is available when the accused genuinely believed the complainant was of legal age, and that belief was reasonable under the circumstances.

The correct answer hinges on the factual basis that if the complainant was actually 16 years of age or older, the accused could potentially use the mistake of age defense, assuming they had a reasonable belief about the age of the complainant. This aspect emphasizes the critical age threshold in the law where individuals at or above that age can legally consent to sexual activity.

In contrast, the other statements express misconceptions about the applicability of this defense. Knowing that one is engaging in risky behavior or not intending to engage in sexual activity does not negate the legal consequences when the age of consent is concerned. Also, simply being unaware of the complainant's age does not qualify for a defense unless the accused had a reasonable basis for their belief about the age. Thus, it is the factual verification of the complainant's age being above the legal threshold that supports the appropriate use of the mistake of age defense, reinforcing why the mentioned option stands out as the correct choice.