My Six Month Old german Shehperd Weighs 51 lbs(23 kgs.) is it ok or is he verry skinny he is around 59 cm tall?

thats a little skinny in my opinion but if his parents were small then it should be fine. i know my german shepherd was 130 lbs at about a year and a half but he was on the smaller side for a long time. some GSD's just take a little long to grow