Is a 5.8 pound ragdoll kitten at 5 months very small?

I love him so much , I’m just wondering if he will be big or small! The vet said he would be small and done growing at 10 months . However I thought ragdolls grew until 4? Rollo is from a very reputable breeder . Let me know how your ragdolls grew ! Any runts that surprised you?