The timing lines up... you, my friend, are experiencing the horrors of the green cheek puberty.
I would encourage you to google and read up on bird hormones. At around 12-18 months, green cheeks will start their puberty. It's temporary--but can last a while, and it's not pleasant.
It's important that you understand that it's not personal. Your baby still loves you--he's going through wild mood swings and emotional turbulence!! Be patient with him, and adapt in whatever way will allow you to continue interacting with him, even if that means talking to him and spending time with him while he stays in his cage. Try not to get angry or resentful.
None of these suggestions are probably going to stop his biting behavior, but they might improve things, and birds will go through periods of high hormones throughout their lives so these tips will be helpful in the years to come.
1) He should always get 10-12 hours of relative darkness and quiet every night, whether that means you cover his cage or put him in a dark room for bedtime.
2) Seed diets are high in fat and can cause hormonal imbalance as a result. Lots of veggies and a pellet diet can improve hormonal behavior.
3) Always discourage nesting behavior. Don't provide small, dark nooks. If he seems to be nesting in something, like a bowl or basket or hut, remove it. Nesting behavior includes panting, slow head bobbing, and violently protecting the nest.
4) If your baby rubs his butt on objects in the cage, remove those objects.
As for dealing with the biting, I have two suggestions. The first is shunning. If he bites, tell him a firm "no" and put him on a neutral perch like a chair back or table (DO NOT put him in his cage), and then turn away and ignore him for a minute. If he flies to you, put him back on the chair/table and continue ignoring until he serves his time out. It's important not to yell at him, and it's also important to try not to yelp in pain if you can avoid it, because any reaction beyond a boring "No" and brief shunning might be just fun and interesting enough to encourage him to bite more.
Shunning can only go so far though, and some hormonal birds will bite compulsively. It's important to be consistent with the shunning, but I've also heard of people having great success with bandaids to protect their hands or other common target areas. Gloves might be too scary but a bandaid or two can cushion your skin from the bite without causing your bird to panic.