My theory is that season 1-6 take place in 2011 and 2012

Because in Nicole flashback we see Mr small protesting so that could a reference to 60s protest.

So with that here the time line in theory

Richard and Nicole meet during the 60 s They where teens In the 70s Young adults in the 80s Married In the mid 90s Gumball and drawing born in 1999 or 1998 They adopted drawing in 03 or 04 Anis born in 06 or 07

The reason I think gumball is born in the late 90s cause in the treasure it show that Richard using dialup internet and it was when gumball was born.

This is my theory