This is a similar situation to someone else on this forum, he studied economics but has the advantage of having taken a number of math classes, and he claims to have scored a PGRE score of 960, which murdered a hell of a lot of people i know with bachelors degrees in the subject (not the least of which is myself...yikes!). I have to say this kind of situation makes me so curious--why music all those years ago, why history after that, and why physics now? Especially with your GPA are you not somewhat worried that maybe you are just not a driven student in general (this is not an insult but an observation, my undergrad GPA was 3.0 and even worse in my major and i can definately say that it was precisely because i was lazy). Moreover how do you know physics is it for you without ever having studied it--did you think history was your calling when u applied to penn? How do you know that you wont feel disillusioned with physics too? I know this sounds harsh, but at 28 and with 2 unrelated degrees with which you are unsatisfied and no experience either professionally or even scholastically in a technical field (not to mention i am guessing some significant student debt), I would recommend doing some serious soul searching before embarking on something as time consuming and competitive as physics. With that said, and before i start sounding like someone's dad, it is always worth remembering that Ed Witten's bachelor's degree was in journalism--and hell, John Nash's kid didnt even get a bachelor's degree before he went into grad study in math (as rumor has it), so if you are sure go for it, but think critically first.