Is the aqiqah of an adult for himself (something) proven?
It is proven within the Sunnah from two chains of transmission on the authority of Anas ibn Malik that the Prophet ﷺ performed an aqiqah for himself after being sent as a prophet. Some of the salaf held this opinion and acted accordingly. Ibn Seereen said, “If I knew that he (his father) did not perform an aqiqah on my behalf I would perform it for myself".
Al Hasan Al Basri said, “If an aqiqah was not performed for you, then perform it for yourself even if you are a man.”
Moreover, it is recommended that a man performs an aqiqah for himself as a substitute for his father, due to the naseekah (aqiqah) being obligatory on the father, and remains so even after reaching old age if it is easy (for him). If he does not do so, a substitute/replacement for him is allowed, due to this being worship related to wealth in which a substitute (to carry out) is legislated. Worship related to wealth allows substitution therein e.g. zakat, donations, and similar to that from worship.