My girl had the Specialized at about age 4 but had grown out of it by 6, knees hitting handlebars etc., she's not exactly big for her age either. I tried her on various 18" bikes but they were all too big so I had to get her another 16" bike from Decathlon.
The decathlon has a bigger size range, was half the price and is perfectly good enough for what she needs. Only better feature on the Specialized is the reverse pedal braking but she gets on ok (ish) with the oversize easy-pull leavers on the Decathlon.