Not that I care much about titles, but since I discovered that in my workplace, becoming one is a promotion that comes with a few extra $$$, I'm asking myself that question.
Looking around me and on professional social media like LinkedIn, there doesn't seem to be a pattern. I see "kids" with less than 10 years experience with a "senior" title. I see others with lots more experience who're merely "engineers". I've always had an issue with this title as it would put me on the same level with seniors I work(ed) with, who I find much more experienced and skilled than I am, and that will always be the case until the day they retire.
Anyway, just wondering. It all seems so random.
I design aqueducts in a parallel universe.