If you have previous experience with a language and feel that lessons are too easy, there are several ways to advance more quickly, skipping ahead by unlocking grayed out skills and lessons.
Link to the explanation:
https://support.duolingo.com/hc/en-us/articles/204641974-How-can-I-skip-the-basics-

Try taking a proficiency test to find out your actual level.

https://www.transparent.com/learn-french/proficiency-test.html

You can take a test on each checkpoint (I'm not entirely sure if this is still a feature) or you could deactivate and reactivate your account to take the placement test, or you could click on the test on your profile.

Here is a new feature I've been lucky to be chosen to test which does just what you are asking for. I find that in the French course I now do what at other times would be very difficult to translate sentences with very little thought. I've internalized the grammar etc.

https://www.duolingo.com/comment/25615588/Upcoming-Feature-Skill-Levels