No, I think it is not to early ... but relax and do not plan to much. do not plan every single travel day... the best is: just look around now, find nice places in Europe you want to see.
And then when starting your tour, visit these places ... it will be fun.
But you will always meet other travelers during your tour (hostels are nice places to exchange ideas, places you must see and so on...).
And sometimes you join them, when you have a good understanding and the same route for some days...
So enjoy the feeling of InterRail: being free !!
Don't plan too much!!
And if the weather is bad, take a train and travel to a country where the sun is shining !!