Pah. My oldest wouldn't ride her balance bike ever, it was too wobbly. She rode a pedal bike with stabilisers on it all over the place, and as I kept surreptitiously raising them she got better at riding. Managed to persuade her to ride without a few weeks before her 5th birthday and she did it no bother. Until after about 10 mins she forgot to brake, hit the car and faceplanted. Now she's refusing again.
Her younger sister was on the balance bike at 18 months and 6 months later was scooting about properly feet up. Kids develop differently, don't expect the same schedule from them! Similar story with other physical tasks - youngest has always been more physically capable. Took oldest one far longer to learn stuff like two footed jumping etc.