My child is grown up already. Can I still do Aqiqah for him/her?

Aqiqah can be done for the child even if it is after many years.

Source: islamqa.info (https://islamqa.info/en/answers/227/performing-aqeeqah-for-oneself-and-older-children-and-borrowing-for-it)

Do also refer to Asatizah who are proficient in Fiqh.