I saw them graduate high school in the 70s and then have have Lisa in the 80s, and homer was a grunge star in the 90s. We don't need a strict timeline.

Not only that, but they've explicitly changed their ages/backstories at least twice already

Meh, just make the show funny

Comon now, let's be realistic lol

Is anyone still watching? like... who?

There's an episode where they pretend the Simpsons are a real family and do an "interview" of them since they gained fame. In that episode, Homer says something like "people think that I use growth hormones to keep the kids young, but how am I supposed to fit all three pills in their coffee?" At the time, I believe this was supposed to (jokingly) explain their everlasting youth.

(I tried to find this clip on YouTube but can't remember the details well enough to find it)

Single income, though there is a recent episode in which Bart goes to see Homer at work and realizes how much money Homer makes for how little he does. Bart loves the concept of Homer's job, then assumes this is the job he'll get after Homer retires and he feels good about his future. Then there's a literal song and dance from a janitor about how that type of job no longer exists, and when Bart is old enough to work he'll be worked ragged. s33e22 Poorhouse Rock

Last I knew they were still single income.

Homer was forced to go to college and take relevant courses, but not graduate AFAIK. Pretty sure he only passed those courses by cheating even.

I've seen several episodes about how he got the job, but the method that sticks in my mind is groveling.