Welcome to the wonderful sport of two wheels.
Dirtbikes are quite fun and are better than no other training, they will teach you the same basic principles you would learn on the first day of a street bike, brake modulation, clutch, gearing, throttle, basic balance issues etc.
Ride it, practice, take the MSF course as soon as you can and then move on to a street bike which would make you happy. Bigger is not always better, some of the best times on the motorcycle I’ve ever had are on my 38hp Motard and some of the purest riding feel was on my Ninja 250.
Gundam, we should go 250 riding if you ever find one for yourself :lol