I was born in March which is later than most of the other kids in my grade.
My birthday is later in the school year compared to most of my classmates.
この場合、次のような言い方ができますよ。
ーI was born in March which is later than most of the other kids in my grade.
「私は3月生まれで、同学年の他の子たちより遅い方です」
later than で「〜より遅い方」
ーMy birthday is later in the school year compared to most of my classmates.
「私の誕生日はクラスメイトと比べると、学年の終わりの方です」
later in the school year で「学年の終わりの方」
ご参考まで！
カナダ 
