I’m struggling to read my budgie

I got my little guy approx 4 weeks ago when he was roughly 9 weeks old, I’ve managed to have him hop on my hand with/ without millet, he loves to have his neck rubbed, he now comes up to me when out of the cage and will hop on my hand to be transported around. He’s now about 3 months and as of 2 days ago he’s started trying to bite. The first 2 times was when I was petting his neck/ head so I stopped doing that and just now when I’ve put my finger at his feet to perch he has gone to bite me. He has never showed this type of aggression usually he will nibble at my finger but this is different. I can’t help but flinch every time because it does scare me even though I know I should keep calm. My question here is how can I read him better when he wants attention/ wants to be left alone. I usually thought him being on his front perch meant he wants attention but that’s where he was tonight when he tried to bite. Can anyone tell me signs for when they do want attention and signs for when they don’t? Is this normal for this age?

TIA