haha i think its just a phase they go thru. cos they never worn shoes previously so they just dont feel comfy with it yet. but they'll get used to it.
your son is walking steadily now already right?? i think can let him wear the harder soles type of shoes. cant really go by age, cos like some todds learn to walk steadily earlier(arnd 1 yo), some only start walking steadily near to 2yo, so hard to guage.