What is the ruling on one who kissed his paternal uncle's wife, being sixteen years of age, for the purpose of lust?

Whoever reaches sixteen years of age is considered an adult and accountable. If he kisses a woman unlawful to him, he has sinned, and he must offer sincere repentance. This means abandoning the sin, regretting it, and having a firm resolve not to return to it. He should also draw closer to Allah through acts of obedience and good deeds, for they expiate evil deeds, as Allah the Almighty says: "Indeed, good deeds do away with evil deeds."