I will share how someone was surprised to know I am his senior. Do you feel he was right when he said that?

Back in 2017, when I was in 12th grade,there was a boy named Mukesh who was in 11th grade and was new to our school. But he was very tall with a height of 6'2 and he was the tallest in our school even taller than the tallest boy of our class named Saishyam who was (still is) 6'1. Being around 5'8 I used to often compare my height with him and irritate him saying you are so tall. I used to also call him Biggie because of his big built body but he used to think I used to call him as the great rapper Biggie Smalls haha. Even though he was bigger built than me I used to still try to intimidate him too showing my fist going fast towards him. One day during morning prayer in our school ground he asked me my name and grade. I said my name and I was in 12th grade. He was surprised and said 'I can't believe you are my senior. Till now I had been thinking you were some 7th or 8th grade boy because of the way you behave.' Then another 11th grade biy who knew me since long time said him 'not even 7th grade, he acts like a 3rd grade boy.' Hearing that Mukesh laughed hard. I found it funny and laughed too hahahaha.