No, Duolingo is not for all ages, the Duolingo Kids app is the product designed for kids. It's similar to Youtube in that regard. An "Everyone" rating on play

No, Duolingo is not for all ages, the Duolingo Kids app is the product designed for kids. It's similar to Youtube in that regard. An "Everyone" rating on play store doesn't mean an app meets regulations related to user age, you need to read the EULA to understand where an app stands legally. For example: letting the user upload a photo avatar runs afoul of COPPA. As for why you're seeing that ad, it has to do with browsing history tracking by ad networks... (I started to get contextual ads after looking at a specific niche elsewhere myself) (Disclaimer: my brother works at Duolingo)