Indeed that point is interesting, my observations are (not that I have a ton of them), but, that the "older generation" folks would stick to their native language, whereby the younger folks kind of flip back and forth.
True and it also depends on the person's command of the language and their environment. For e.g. Miami. Even some of the older folks you will hear mixing in some English. However, not from the ones who have been living in Miami for over thirty years and speak no English at all. That is incredible. In my opinion, I think it is better to speak one or the other. If one has a good command of both languages there is no need to go back and forth.
-MP.