Hi. :]

I'm 17 years old and I feel like my personality's a mixture of everyone I've ever met or seen whether in real life or in media like anime, books, music & films, it's almost like every week I change somehow, and it definitely isn't a conscious effort. Throughout my life it's like I adopted a trait from here, a trait from there and kept activating and disabling them and the result is who I am today.. I hope expressed it right.

I wonder whether this is normal or it's a personal flaw like me lacking a personality, being easily influenced and such. I thought it could be an age thing, I hope it is.

Pretty normal, actually. Most people are like that - they adopt traits they see in others, consciously or not, usually because they admire them.
Additionally, you aren't done with puberty nor childhood. Both are stages at which we build and alter our personalities based on our surroundings. From what you've described, it's nothing to worry about.

>>1 like what >>2 said, it's normal, your psych (your personality,) is made up of your experiences. If you think about traits in general, most personalities have similar traits, it's combinations of those traits that make your personality unique. Your personality changes as you go through life as your learn new things and change so don't worry too much about it, just keep working towards the "you" that you want to be ^^