"This is my first time hearing it" is very natural. "hearing it" is a gerund clause

It’s what people say but it’s not grammatically correct. The better way to phrase it would be “This is the first time I’ve heard of it.” And well, it is a sentence in present where you are talking about what you have just recently heard!

I believe that would be better say " this is the first time I hear it" , but in English there are many ways of saying things. However the sentence is grammatically correct.