A person can have unlimited blogs. It’s just a matter of time and attention that you need to dedicate to each blog that will put a limit on how many blogs you can manage.
If you delegate and outsource everything from writing articles to optimizing your WordPress site, then you can run many blogs.
I personally run about 7 blogs nowadays, the number varies if I decide to sell one and invest more time and money into others, or if I want to buy a blog to increase my portfolio.