"I like to learn too!"
Translation:גם אני אוהב ללמוד!
It depends what you want to qualify. Typically, גם אני אוהב ללמוד - I, too, like someone else, like to learn. אני גם אוהב ללמוד - in addition to other things that I've told you about myself, I also like to learn. אני אוהב גם ללמוד - in addition to other things that I like. But all these forms are correct, and in daily conversation they may be used differently, with the appropriate emphasis in intonation.
The English sentence here is ambiguous. The English sentence could mean either "I like to learn (and other people also like to learn)" or it could mean "I like to learn (and I also like to do other things)."
In Hebrew, the placement of גם is much more restricted. In Hebrew גם always goes right before the thing that you mean "also this"
so, גם אני אוהב ללמוד means "I like to learn (and (and other people also like to learn)"
whereas אני אוהב גם ללמוד means "I like to learn (and I also like to do other things)."
In English, we deal with this ambiguity by where we put stress in the sentence. It's kinda difficult to type out what I mean with this example from duolingo, but consider a different example.
"David also went to New York" is ambiguous between whether the word also means "other people also went to New York" or "David also went other places." And "David went to New York too" works the same way.
We can deal with this in English by stress. Here, using capital letters indicates stress:
1) David went to Chicago. David also went to NEW YORK. / David went to NEW YORK, too.
2) Susan went to New York. DAVID also went to New York. / DAVID went to New York, too.
But in Hebrew, you would deal with this based on where you put גם.
1) David went to Chicago. David also went to NEW YORK.
דוד נסע גם לניו יורק
2) Susan went to New York. DAVID also went to New York.
גם דוד נסע לניו יורק
Anyhow, this is an annoying item in Duolingo because there's no way to know which meaning of the English sentence "I like to learn, too" is intended.
To get back to Celioluzverde's question, there's not one simple rule for where to put "too" in English. You can put "too" in lots of different places, and the meaning it has in the sentence depends on what other word(s) get emphasized. I'm sorry that it's not as simple in English as it is in Hebrew...
That's a different meaning of "too". Yes you're right that מדי modifies an adjective, for example גדול מדי means too big. This is "too" in the sense of "excessively", corresponding to zu in German /trop in French, etc. What we have in the sentence here is "too" meaning also, corresponding to auch / aussi etc, which is only translatable into Hebrew by using גם .