Not true, up until about the mid 90's they thought that , but after better research and equipment had been developed, it was determined that Jupiter has a core which eliminated it from being a failed star. The original reasoning was aside from the violent nature of the planet most solar systems are bi~star solar systems, meaning they have 2 suns. Ours is in a minority because it only has 1.

No it's a planet. Any bigger and it would be a star/ failed star.