adult adoption question

Thanks in advance, first of all, is this the best thread to ask this question? I am in my 50's and considering asking an adult in their 20's if I can adopt them as a child. Their is an emotional angle for me as this person is the same age as my child would have been who passed away. We have known each other for several years and are platonic. I'm looking for others who have been in this situation would be willing to share their story. Much appreciated. Cheers.