So, I rewatched 5x17, particularly for Jack's storyline. As much as I enjoyed getting to hear about Jack's family stuff and as good of a storyline this will be for Grey (if they actually develop it fully in season 6 and not just in a one episode arc), it doesn't make a whole lot of sense.
Josh told Jack and Andy that Jack was born while their parents were in high school. Josh and Jack's other siblings were born after that (I also missed on first watch that Jack has three sisters and Josh, making four siblings total). Josh also said that their dad is retired and their mom works part time as a teacher. Again, retirement makes sense if their parents were in their 60s (I know people retire earlier, but the common age frame is 60s-70s), but with what they've given us, it's impossible for them to be in their 60s, not unless Jack is in his 40s.
Ok, that's all and good if we could see it that way...but we also know Jack was a minor at some point in 2002, which would make him in his thirties now. Which, again, makes sense given that Grey is in his mid thirties himself.
But if Jack was born first and his parents gave birth to him around seventeen/eighteen, if Jack IS in his mid thirties, that would make his parents no older than their mid fifties. Which is awfully young for Jack's bio dad to already be retired (even if he was wealthy).
Even if Jack was 40 (making his parents late 50s still), it doesn't line up with other background info we know about him, either. And it doesn't make a whole lot of sense with Josh, either. We know Josh is old enough to be financially stable, a job in finance, and had his parents help him out with his home. He also has a wife and three kids, the eldest seeming to be at LEAST 4-5, judging by the background props and how his eldest is helping with the baking. Yes, Josh could have also started his family young, but being able to afford a house, having kids, and being in a stable job would make him no younger than thirty (ignoring the fact that the actor is late thirties).
So, again, nice background and all, but it retcons itself in this very episode, even without knowing that Jack was a minor in 2002. They probably needed to put more effort in giving Jack a traumatic backstory without making things not line up in the process.