Earlier this year I looked at my duome page and said to myself, "If I do a good bit of practice each day, I should be able to reach 7000 crowns before the end of the year." That happened this morning and I feel a bit of pride about how much I've been able to learn and expand my thinking beyond the borders which knowing only one language can impose.
When I first started using Duolingo, it was to help me in my efforts to learn French as someone who was past the age of 40, an age when it is felt that new language acquisition is very difficult. I can't say I've disproven that assumption, as I have only rarely spoken the languages in which I have at least some passive fluency in reading and listening. But I do read from French and Spanish rather well. Portuguese and Italian are less fluid.
Esperanto is a special friend. Its simplicity provided me a language that I was first able to think in for extended periods of time without slipping back into my native language, English. I do feel it has utility for an older language learner trying to escape from monolingualism. The simple grammar and word-building features in it can provide a means to play with language and how it can shape our thinking.