Can a 7-m.o. already use a walker? We're planning to use the traditional one which is made of ratan.

Yes yes. This is cool. Usually my kids use them from age 5-6mths when they can hold themselves independently. In this way, they can learn how to sit straight too. This is if you are using walker. This type I've not seen before but i think it will really help them to walk. Give them more calcium rich food to build up their bones.