The height of fashion means the clothing that was the most popular during a certain time. For example. "Suits were the height of fashion in 1920s america.

Have set a new trend can mean that somebody made something popular. "_________ tiktoker set a new trend by doing a new dance"

Ahead of it's time. Or ahead of their time. Means that something was very well done for the time. "The iphone was ahead of it's time" "Albert Einstein was ahead of his time". These things were the first and I took time for the world to catch up.