I agree with Karin.
There are great masters in almost every genre of painting from portraiture, to environments, to wildlife, to still life, to landscapes. Further, by Old Master, I don't mean only those realist painters from 1400 to 1900. There have been masters throughout history painting humanism, realism, impressionism, and all the other isms. Pick your poison and learn from them. It does not mean you have to adopt their style, but for the beginning artist, you sure can learn a lot.