I have a dilemma when my students ask me questions about something that is beyond their level. From one side i don’t want to leave a question unaswered, besides I believe that is how you leran a language: you have a question, you answer for it.
From another side I would have to explain so much that is not relevant to what we are doing right now. Also my I am sure my explanation will be too confusing for my student just because he or she haven’t gained enough knowledge for that.
so, tutors, what do you do in such situation?

In my case its simple. I teach using no translation, or VERY little. Therefore, if I explain something, they will know that they need more knowledge in order to undertanhd that.

Discourage your students from wanting to run before they can walk, by NOT translating.

I usually compliment them on their question, but then tell them it’s outside the scope of that particular lesson. This should leave them feeling positive and encourage them to ask questions in the future, which as you say is how you learn a language. If the student seems genuinely interested in getting to the bottom of the matter, you could always message them a few pointers after the lesson.
Hope this helps.

explaining to them that it is not relevant to know the answer right now, but may be later on.

you should explain a little and tell they need more knowledge to understand and to attend next classes to learn more :D