Sometime in the 1980s: 22 year-old Greg plays a show in Beach City, meets Rose.

Sometime after that : Greg records the video for "What Can I Do For You?", where he is seen wearing his yellow star tee-shirt.

6 months to a year after arriving in Beach City: Greg gets his job at "It's A Wash". I assume this is after the taping of the video because Greg never gets his shirt back from Vidalia.

15 years before the current day: The mud-nado drives up demand for car washes

14 years before the current day: Rose gives up her physical form to give birth to steven

Sometime after that: Greg builds the beach house in front of the temple.

6 years before the current day: Steven turns 8 and moves in with the gems

If the current day of the show matches with our own timeline's (our technology matches at least), then Steven was probably born in the early 2000's.

Because Greg doesn't look like he's in his 50's, he and Rose probably met in the late 80's. If they met in '89, when Greg was 22, then Greg is about 48 now. By coincidence, Tom Scharpling, the voice actor for Greg, is 47.

That also means that Greg and Rose had almost 15 years together before she gave up her form.

There's not that much new info here from the most recent episodes, I just felt like working through the timeline.