Am I fat

Weight itself doesn't determine how fat you are. It depends on your body fat levels and how much muscle you have.

I’m 13 5’4 and 150 lbs and I fat?

And bone density - you can be the same height and clothes size as someone else, but be 2 stone heavier; all down to bone density.
At 13 you're too young to worry about this stuff. So long as you eat a balanced diet, drink plenty of fresh water, sleep 8/9hrs and take some exercise (walk the dog for half hour or so, etc), then you will be just fine. BMI is not a one size fits all. Don't ever mess with your diet - it's dangerous. It is good to talk though .

Pretty sure bone density can't make a 28lb difference.

I speak from experience, friend ...

And how did you measure the weight of each others skeletons and deduce a 28lb difference?

Oooh! Nothing as scientific as that . Just two friends, same height, same shoe size, same clothes size - but - nearly 2 stone difference!?! How about that?!?

Yea not scientific so don't come around and start making claims backed by nothing except anecdote. Ur fat distributions were different not one skeleton was 28lns heavier, to even have a 28lb skeleton you would have to be 90kg and the other person would be 0kg.

Woah! Steady friend - not making any claims. Just that bone density can also have an impact on weight, as can size of bones and muscle etc. Poster is only 13, so long as they are eating balanced diet, some exercise, etc they are probably not overweight. Dangerous to mess with your diet unless a qualified Dr is involved. BMI is very misleading if taken on its own - don't you agree?
Let's keep this friendly and help Poster feel better about themselves, right?

You have a very unhealthy weight, according to the nhs bmi you are overweight for a girl and very overweight for a boy. Basically yes you are fat if that helps you understand better, you are unhealthy and don't want to risk getting diabetes or some other bad illness.
What's your diet like and how much exercise do you get every week?

We don’t really know if she/he is fat. BMI has little bearing in this context as we don’t really know if their weight is mainly muscle or fat. In other words, we don’t know their body composition, so you can’t come to that conclusion and state they are fat based off of a BMI index that doesn’t apply to this person due to our lack of knowledge in regards to their body composition. Now, it’s fair to say they are LIKELY to be fat as that weight, assuming the OP is a boy, is not likely to be mostly muscle due to their age and the whole puberty thing. But it’s possible that it is mainly muscle as evidenced by...well, let me go with a famous person. Type Mike Tyson age 12. He was about 5,8 and weighed 190 pounds at age 12. Technically, that’s obesity. But you tell me I’f he’s obese just by looking at him.

Case in point. Give advice based on the facts presented and the likely/unlikely scenario. Don’t state things without undeniable evidence.

I’m 13 5’4 and 150 lbs and I fat?

If OP had the muscle of mike tyson which would take a lot of hard work, dedication and knowledge, I don't think they would come on TSR asking if they're fat.