Alot of cage aggression is coming up in posts lately but alot of it might be due to the fact its spring and birds are more hormonal with their desire to mate at this time which makes their behavior different on many levels.
I like to tell people to be patient during this time because they cant help it. Still talk to them open their cages and allow them to come out on their own and then get them to step up and take them to another room to spend time with them actually does really help alot during this time.
My quaker is 4 also a rehome and has been horrible this year but he is getting better and I have seen it before so I know it will pass.
On another note if this is an ongoing thing non spring related it might be that he is being over stimulated by being out and handled too much. If thats the case then take him away from his cage for short intervals only and look for body language that lets you know he has had enough playtime and wants to go back to his cage. If its fun and positive he will be more willing to want to work with you when it becomes a chore they do opt to go to great lengths to not want to do it.
There are a multitude of reasons why a quaker gets cage aggresive from not getting enough sleep to being territorial. Yet everything and anything can be fixed with patience and steps to correct it.
good luck