I think you are right about what you said here concerning age, it plays an important role on how a Bitcoin investment should approach his investment, just as you have said already, you can't expect a 70year old Bitcoin investor still planning on holding for more than 10 years because he knows that he has a limited time, unlike those that are in their 20's.
But those in their 20's don't have to buy only the dip, they just have to buy anytime their discretionary income is available, but if their is a dip in the market they might seize the opportunity and buy aggressively if they have their reserves funds to do so, because they have quite a lot of time to reap from their investment when bitcoin has risen up to a million dollar or more.
No matter the age, it's still very wise to invest in Bitcoin regularly when you can and use market dips as a chance to buy more if you have extra funds set aside cos nobody knows how long they have. Someone in their 20's might not necessarily live longer than someone in their 70's. What really matters is the goal the person aims to achieve, his/her financial situation, and how much risk they are willing to take