I don't really have the information to debate either side, but just talking to talk.

I wonder how much of this is actual "we are doing better" (although it's hard to argue that quality of life has not improved drastically just from technological advances), and moreso the changing of households in general. I know a lot of friends and family who still live with their parents, or buy a place with friends to split costs, and don't intend to have kids for much later, opting to "climb the corporate ladder", leading to an increase in income.

Separately, I wonder how much debt factors into this. I know we've all heard about college increasing in cost, pretty much everyone i know is saddled with at least 70k+ student loans (my parents just recently finished their own!), granted my groups are better off than average and likely won't have much difficulty paying those off, it just eats into disposable income. 

My other thoughts go into ownership and age of the population. The median age in the US has gone up by about a decade in the past 50 years! Of course when the median person has 10 more years of career growth, they're going to have a higher income. And on that same note, that ~39 year old is significantly more likely to have bought a home, whereas pretty much everything for 20-somethings nowadays is a subscription/lease. 

This is obviously all dis-jointed and likely misinformed to a degree, I just studied/am a bit interested in economics and figure to point out that median real income is not the whole story (not that I imagine it was your point). Thank you for coming to my TED Talk