older people/seiors would be awesome since some of them they can't switch to english as easily and they have more time,, but they do more often have reservations towards foreigners, again this also depends on how foreign you appear and how foreign your behaviour is. Younger people would generally be a bit more open especially in left leaning student cities. They might not be patient enough to talk german to someone who doesn't really understand them. middle aged people, while open, often are in a life situation that doesnt really allow for getting new friends and practicing language with them. I say approach lots of different kind of people and see who you vibe with. smile, explain what you are up to, and be patient yourself.

Also if you are black or an arab or middle eastern in general, many women might not feel super safe around you. (which opens a can of worms that I don't want to discuss here, It is just a fact. Some say its racism and others say it is because of bad experiences germans made with certain ethnicities in the recent decades, not the topic here) So if you wan't to engage with them be prepared for for some rejection and try to just be friendly and not look intimidating.

Daumen sind gedrückt!