Stuck at 60%
I have one problem: I stuck at 60%. Is it possible to get a higher level? I have been learning English for 2 years and I have been increasing my intensity to 100 Points a day. But now I am at 60%. I have been there for three month. Is this normal?
You can't get much higher, no.
Remember that Duolingo doesn't teach you the whole language -- it doesn't have the complete grammar and vocabulary of the entire language stored. So it can't really tell whether you know all of a language or not, and the fluency percentage has a maximum that it will reach, depending on the course. Usually around 60%, I think, though I've heard of 70% before as well in another course.
So your number is probably not going to change any more, simply because Duo can't teach you any further -- you have learned all that Duo has to offer and if you want to improve, you will have to look for external sources.
But even if you do improve, Duo can't measure that and so the percentage here will stay.
60% is a lot and it is normal not to go up after that level. You can probably increase it a little if you redo the whole tree.