na-adjective, noun
child born in the second half of the year
Refers to a child born between July and December, often in contexts like school year cutoffs or age-group sports. The term is somewhat niche and may not be widely known outside specific communities.
年弱の子は同学年の中でも体が小さいことがある。
Children born in the second half of the year may be physically smaller among their grade.
彼は年弱だから、まだ6歳だけど来年小学生になる。
Because he was born in the latter half of the year, he is still six but will start elementary school next year.