On the question of at what age one should start to read classics: Ideally you should be very old, so you can nod in agreement with all the wisdom that the book is spreading over you. However, since there are quite a few classics, this strategy means that you will not read as many of them as you would like (at sixty-something).
It has been observed in many countries, not only Russia, that feeding lots of classics to young children seems to have an adverse effect. Yes, they look boring at that age. And remember, Dostoyevsky wrote in installments. Each chapter of a novel would be published in a magazine, so the readers would consume the story at their leisure (if that is at all possible with a Dostoevsky story).
I only started reading Russian classics when I was 24, and by that time I had apparently gained just enough patience to accept the drawn-out descriptions and plots.