“For stars with similar metallicity to the Sun, the theoretical minimum mass the star can have, and still undergo fusion at the core, is estimated to be about 75 times the mass of Jupiter.”
This one is six times the mass of Jupiter, so maybe 12.5 times larger to ignite, rough estimate.
I don’t even know if it is possible for planets to become stars, even gas giants with the right composition. Stars are thought to form from interstellar gas clouds that become dense enough to start collapsing gravitationally. A planet has already coalesced to a gravitational equilibrium, so I think it’s too late at that point.
I think it is classified as a planet simply because it does not fuse hydrogen, not based on structure or origin.