I am a late late 20's millenial. I saved basically nothing from 22-26 besides some 401k, traveled a bunch, paid off minimal student loans, got my Masters degree at night, got married, saved a little bit for a down payment and bought a house. Since then we have been working hard to save, my company matches 7% in 401k and we max it out and put about 10% more into our investment account. Just had our first kid and we decided to do the single income thing... which was rough. Went from making mid $200s combined to a lot less.
I hope to retire by 55 or the day my eventual youngest child goes to college, whichever comes later. If we stick to our savings plan we should make it, but if the market goes way south, or we have an unforeseen financial difficultly, it won't happen.
I'm going to be real interested in what the long term macro-economic impact is of millenials having dual incomes in the vast majority of cases which is leading to much much fewer kids, if any at all. As a new millenial father, I would recommend to a LOT of my younger friends that they have no business having kids. It isn't going to fit their life and make them happier.