cockatiel being a bully

by charles
(Fayetteville, NC USA)

Hello, i got my grandmother grey cockatiel that she had over 7 years and she wasnt a good bird parent. she didnt let him out the cage, didnt spend time with him or anything. He had a friend who was a cockatiel as well but he died (probably cuz he was really old)about 2 years ago.

So some months ago i recently got him another cage mate (had her 6 months time in another room) who is a female who a little younger than he is. When they are out the cage he may just come over and peck her for no apparent reason. He doesnt like her to be close to him and she may lower her head for a scratch to him and he peck her still. He is very sweet to my male parakeet tiko and sometimes feed him. How can i get him to be nice to female teil as well ?