Awwww....this is such a frustrating situation, for any bird owner. I feel for you.
First I want to ask, have you tried approach and retreat? If you are walking up to the cage and Neo essentially charges at you...turn and walk away...wait a moment or two and try again, and again and again....until you can approach the cage without the aggressive behavior. It's usually more effective if you can read his body language and turn and walk away just seconds before Neo charges the cage bars.
Second, when Neo is out or coming out of his cage, instead of getting your fingers all bit up, you can try to use a stick or perch for him to step on...I have a cockatiel I rescued 2 years ago and he'll step up great for me on a stick I hold, but if I offer him my finger, he squawks and runs or flys off. Makes no sense, as he has learned large vocabulary since living with us, he loves to talk to and with me, he'll get right up close to me and I know he's comfortable with me, but if I offer him my finger to step up on...he just panics and immediately creates a temporary physical distance that's he's comfortable with.
And 3rd...don't under estimate the power of your voice. If Neo is brand new to your home, just talking to him all the time, as you are doing things in the room he's in - will help sooth him as he get's to know you and the tone of your voice. You can tell him about your day, read him a book, sing, hum, whistle, say his name a lot, tell him he's a good boy or a pretty bird etc. And as he relaxes toward your voice and he's able to "study" your body language, he should start to relax and the aggressive charging should subside.
When we got our conure, Franklin (you can see pic's of him in my profile albums) he was just shy of 3 months old. He was such a dear sweet angel. He'd go to anyone and never showed any aggression. My goal was to keep him well socialized, so I encouraged my kids friends to come see him and if I had him out, I'd let the kids (10-17 years old) hold them if they wanted.
Franklin's cage, at the time was in our bedroom set on top of a cabinet, his cage placement was such that the bottom of the cage was about mid chest and the top of his cage was over our head.
About 3 months into owning him, he began to develop a rather...opinionated personality (not uncommon with conures) We'd open the door of his cage to let him out and he'd dart out and run to the top of his cage, where - unless we took the cage down and set it on the floor, we could hardly reach him and he could easily play "keep away" Other times, we'd open the cage door and he'd come and stand in the door way, we'd hold our finger steady and ask him to step and sometimes he'd have to "Test" with his beak before stepping up and sometimes, he'd test and put one foot on our finger, the other firmly gripping the cage and then out of no where...WHAM! He'd land baste our finger with a stout bite!
This went on for several months and although we'd have some good days, they seemed to be spreading out further and further from each other. Quite frankly, we were getting jumpy just offering him our finger. I should clarify that USUALLY...once we got him out of or off his cage, he loved to be with us, we were his human jungle gym and showed no sign of aggression.
I picked up a book about behavior problems in parrots and I read it cover to cover and that's where I learned that his behavior could be associated with his cage being so far above us. He felt like he was king of the world so to speak, the big boss being up so high, so I moved his cage down so the TOP of his cage was at my nose or so.
Of course the first time I went to let him out, he bit me, HARD! I did my very best not to react, and simply closed the cage door and continued about my day, Keeping my emotions out of it, meaning I didn't flip out and start yelling at him, or talking to him in a gruff tone, I just shut the door and walked away. I probably said something like "fine..be that way." I'd try to go back about 15 - 30 minutes later, opened the cage door he came to it acted like he was going to be nice and step on my finger and bit me again! I again, just shut the door. I had decided that if he can't come out nice...he's not coming out at all. And believe me...he LOVED to be out! He didn't always successfully bite me, sometimes I could just tell by his body language...this was going to be a "fail" but I still gave him the chance.
Anyway, It was 3 days, I tried letting him out at least 5-10 times a day, always reminding him to "beeee niiiiiiice...." when I offered my finger...finally...on the third day, I will admit, I was scared, my finger was sore and he was definitely timid...puffed up, nervous, shaking...but I once again, opened the cage door...every time I talk to him, tell him something like "Hi Frankie", ask him if he wanted to come out and play, and when I put my finger out for him, I'd tell him...beeee niiice...he reached out with his beak...he tasted, but didn't bite, he retreated, I told him it was okay, and to come out and play and be a good boy, he came back, he tasted me again, put one foot on my finger, the other firmly on the cage....he puffed, he shook his feathers, he held onto my finger and onto the cage doorway...I bet I stood there 10 minutes, trying not to move, just gave him the time he was seeking to figure out the right answer and I could tell...he was in serious thought...and finally...he let go of the cage doorway and stepped onto my finger with NO BITE!
Oh how I praised him, I could tell he KNEW he did the RIGHT thing and we had a great day!
That was a HUGE turning point in our relationship. Since that day he did "relapse" a few times and when he did I just shut the door and he didn't get to come out and I'd try again later and usually that's all he needed for a reminder.
Sometimes I could tell he was thinking about biting and I could deter him by just saying...Beeee Niiice....and every microscopic move in the right direction I'd praise, by saying "Good BOY!!" and "that's right...beeee nice"
Since then we've sure come a long ways and we don't get bit at all anymore. Not to say he won't, but we don't encourage that opportunity. If he's clearly showing aggression at all, we just let him be and try again later.
I know this is a long winded post...but hopefully it helps a little. It's a lot of work to train any bird....best advice I can give you is to keep your emotions out of it as much as possible. Our human instinct is to get mad, we want to cry, yell, get back at them, take the aggression all personally... it's in our nature, but this has a horribly negative effect in training. (ESPECIALLY birds!)
Good luck, be CONSISTENT and be PATIENT and you will reap the rewards.
Our Franklin is such a fun, super smart and hysterically funny bird. He's developing an excellent vocabulary (rather rare for a GCC) He needed to learn the boundaries and we needed to learn to not "force" our self on him...just because WE want to play, doesn't necessarily mean HE wants to at that moment. We respect that, we haven't been bit.
Take care,
Toni