For me that is slightly disappointing, I find that there is some real character in that accent. From my (outsider's) perspective it is something classic to east coast American cities. An accent that brings forth unapologetic honesty and "bustin' your balls" kind of humour.
It's a social class marker; plenty of people have it, but if you're hanging around a college with a lot of upper middle class teeth gritting cheesebags and hangers on, you may never hear it.
I grew up with a western mass accent, which is a sort of lighter version of bahston with less non-rhoticity. I can turn it off, but lately choose not to, also for social class reasons.
I have an old relative who has the classic, very thick Boston accent. It is always fun to have her say, "park the car in the Harvard Yard", and she is willing to humor us. You are correct that most younger people don't, though some have a less significant one. Accents are disappearing among the young, which is somewhat sad, albeit inevitable. Newscasters never have an accent, most characters do not (and when they do, it's a "difference" of some sort), and people move around too much for them to survive. A Texas accent used to be John Wayne, now it is used on comedy shows to represent the "uneducated, fat, cousin-marrying red-neck bumpkin". At least we have recording technology now, so future generations can hear them.
> Accent is defined based on where you grew up from age 10-12.
Not so. Maybe this is true in many cases, but I personally know of at least one outlier: a relative who grew up in West Virginia, lost her accent to work in radio and news, and when older re-married to a man from Texas with a heavy accent and developed one herself.
It is also the case that many people slip back into accents as they age.
