Interesting discussion. I'm the one who raised lifecycle and human capital thinking, so I will continue from that perspective.
The issue of "saving for retirement," as has already been pointed out in this thread, can involve building wealth, avoiding what economists would call "dis-saving," (= taking on debt), and, finally, actually putting money aside, whether in stocks, bonds or some other instrument.
The issue of whether you can "save more" when young or old, for lifecycle economists, is broader than whether you are actually putting money aside. In general, from the lifecycle perspective, most people will have a greater capacity to "save money" when they are older, and they will have greater dis-savings (debt) when they are younger -- whether it is mortgage debt or student loan debt, to give the two biggest examples.
I, too, saved most of my money in my 20s, before I had kids. But I also took on my biggest financial commitment then, a mortgage, which is a big amount of dis-savings for me.
I'm not disagreeing with you, Leslie; at least not intentionally -- it just seems to me that if you accurately value the balance sheet of an idealized young person, with debt and a large human capital balance, versus an idealized older person, with a somewhat depleted human capital balance, ideally much less debt, and ideally greater yearly cash flows from their human capital, then it is clear the older person has a greater capacity to save (if you define saving as putting money aside.)
(If you define saving as building up an asset you can monetize slowly over time, then perhaps the time of greatest savings is when you are in post-secondary education.)
If you keep spending at a constant $50,000 per year, for example, the idealized young person will likely need to borrow to sustain that level of spending -- while the ideal older person would have the capacity to save a large fraction of their income.
So, it isn't about "excusing people for starting late" -- at least for me -- it is about keeping your lifecycle spending smooth over time.