Bluffing

We have 2 alexandrines one is just over a year old and the other is 8 months old.
The 8 month old one is becoming challenging, biting etc.
I've read a little about bluffing and I would be interested to hear what age other owners birds started this phase, how long it lasted, and how you managed it.

Hi, my Alexandrine is 16 months old. He started what I thought was bluffing about 4 months ago, for no reason he would lunge and be grumpy and get over excited. He would fly to me when I called and bite me. It lasted a few days. Unfortunately I don't think it was true bluffing, I think I still have it to come. Even so I got advice here and was advised to move his perches lower in his cage so us humans were generally above him. Also make sure he got at least 12 hours uninterrupted sleep. Other than that I was firm (I'd already got into a bad habit of covering my skin), but tried not to change anything. I checked he was eating the right amount of the right stuff too.

Every now and then he has a grump on him, he will refuse to step up and one night recently he point blank REFUSED to go back into his cage! He has never done that, even before he was tame. He's also had a couple of days where he's lunged and threatened to bite my hand even though we've worked hard on getting him used to skin recently.

So, not sure if this helps that much, because I don't think I've seen the true bluffing stage yet, but I think something is going on at the moment. Sometimes he just has a real puffed up attitude about him, that he's the boss and we'd better understand! I think the teenager is emerging. If anything I'll up the training if it gets worse and also encourage him to fly as much as possible to get rid of the energy.