"嬉皮模样的年青人" can be translated into English as "a young person with a hippie-like appearance" or more naturally, "a young person with a hippie vibe" or "a young person looking like a hippie".
Here are some examples in sentences:
I saw a young person with a hippie-like appearance at the music festival.
There was a young person with a hippie vibe wandering around the park.
She noticed a young person looking like a hippie sitting on the grass.