My last post dealt with the investment vehicles. You also have to consider the holdings themselves, which you must have realized because you asked about it. Until Kriegsspiel's post I totally missed that half of your question.
Some people are willing to accept more risk in exchange for more growth, and so they'll purchase a little bit of a small-cap index or an international index, for example. You could also dial down the proportion of your bonds; in my opinion, 60/40 is really conservative. If you're retiring at a traditional age it's often important to be conservative, especially since higher returns will mean less to you, but I think MMM followers have a much higher capacity for risk. If another 2008 comes around, and your portfolio drops 25%, you
could always jump back into the workforce, downgrade to a smaller house or otherwise cut your expenses, or pick up a side gig and invest a bit more of your time into it until another 2009 comes around. Your 70-something parents can't do many or any of those things. It would be worthwhile to look around the Bogleheads wiki (start
here) and perhaps post in or at least look through
forums to decide what asset allocation is a good fit for you.