>2. Should school teachers and parents forbid young kids
>using calculating machine before they reach some level ?

I believe so. It is very easy to mistype a key and get a non-sensical result. So, unless the students can manage without a calculator and use it just to speed up problem solving, the calculator may be more of a hindrance than a useful tool.

A calculator does not solve problems. At least not all of them. A student needs to have his/her brains around to use the calculator effectively.

>1. Is caculator suitable for high school students ?

There are too many variables to have an unequivocal answer to that question. I often saw students grab a calculator the moment they read a problem without giving themselves time to think the problem through. So no doubt using a calculator thoughtlessly may help develop poor problem solving strategies. But, e.g., I use a calculator all the time with my 4th grader son. (Altough this is only after making sure he can solve the problem without a calculator.)

I think a single best answer is that this is a matter of pedagogy. If you can make a calculator useful - go ahead and teach them to use it. But mind the time it may take. It may be better to spend the time on the subject matter.