Don't think Jagger would've finally "settle down" if his heart is empty because he can still pretty much have any woman he wants if he just wants to play around, and hit and move on to the next target given his status.
As far as is it true love or not, only the individuals involved really know. And yes, same age, wide age gap, etc., doesn't matter as it's not universal to just one demographic or age group as there are factual data to back this up.