Did the Meridith character on Grey's Anatomy take off ten years before going to !

Did the Meridith character on Grey's Anatomy take off ten years before going to Med School?

I don't understand how she can look to be 45 and just completed her intern year of her residency then have her half sister who looks to be 25 start her intern year the next year after Meridith.

I know Ellen, TR, and Sandra are old as heck in real life but at least with Christina there's the back story of her having her PhD so she'd logically be a little older than her colleagues. But what the heck is up with Meridith? Did I miss her back story? Are she and her half sister only a year apart? Was Thatcher having an affair too?

yeah i thought that was weird too. her parents got divorced when she was five and i guess her dad didn't waste any time getting remarried because when molly (mer's half sister) was admitted in season 2 im pretty sure she said she was 24 or 25 and that kind of makes sense because i think most of the interns are like 29 - early thirties. but like i said he must have been really quick in meeting susan and having a baby. it's weird. oh and btw i'm like 99% sure that she only went to europe for like 2 months because then she came back b/c her mom was diagnosed with alzheimers and that's when she decided to go to med school. i guess to make her sick mom happy or something.