Mean lovebird- what is this bird's reasons?

I got a lovebird about two months ago that was really, really nice from the beginning. It was about three months old, but unfortunately, it died from poisoning. I just got another about fours weeks ago, and when I got it, it was seven weeks old. It is pretty mean, and bites me all the time. Is it going through adolescence, or is it just the temperment of the bird? Can the meanness be waited out, or is it just a mean bird? The breeder did include that it stayed in the nest five weeks instead of four. Is that causing biting? Will it cause something else?