Ok, let's look at this, though. You're a 23-24 year-old who is either coming out of college and entering the work force or you're coming out of apprenticeship in the trades or something. You get a place.....can a grown adult in today's world function without a cell phone? I'd argue no. This isn't 2004 when every place had a land line and some people were starting to get cell phones for convenience. Now, as for the higher end phones, there's some argument there, but there's also a pretty healthy market for used iPhones and high-end Androids.
You also throw in "flat screen TVs" as if they're some high-end luxury. They're a luxury in the sense that nobody needs TV to live, but on the whole, it's pretty cheap entertainment.....and good luck finding one that's not "flat-screen".
Some of this stuff is the "start-up" cost of adulthood. When you're living at home or in the dorms, you generally have a lot of things simply because of those arrangements. Dorms will give you a bed and a desk. You live at home, there's some level of furniture there that parents have presumably provided. Move out and get your own place and that comes with a need to get some "stuff". Depending on who (if anyone) you're living with and what they have, you may need furniture, a bed, dishes, towels, sheets, small appliances, a TV, etc. Might even need a car. A kid in that scenario probably shouldn't spend $20k on that stuff, but it can be a good amount of spend in a pretty short time and then, from there, you start to accumulate stuff in life like everyone else.
I lay that out not to be all "poor Millennials, what a challenge", but rather to point out that every generation has "start-up costs" to living on your own. It's something they have to budget for, but it's the kind of thing that generally prevents people just starting out from doing things like maxing IRA/401k contributions......but it's temporary. So the Millennials are currently 18-37. Kids in school or scraping buy on entry-level work simply aren't going to have retirement savings yet. Get into your mid-20s and you're still in the "start-up" phase. Hopefully at that age, they're starting to put money away, but savings levels will be low. Then you move on and hopefully get a lot done in the later 20s and 30s. It's life. I'm Gen X and went through the same stuff. I was no expert at those ages and I'm sure I didn't make optimal moves, but wife (no pics) and I went through grad school during the early part of our marriage and some of the better income came later.