Rather than age, I'd say it might correlate more with how recently they got into the hobby, especially if income is not an issue. This applies to hobbies in general and not just keyboards.
The first phase often includes an explosive buying period where the neophyte tries out everything and attempts to 'catch up' to others who have been at it for years. Everything is new and shiny, and expense is no obstacle in the pursuit of the ultimate keyboard experience.
Since you mentioned cars, I'll compare my car stuff to my keyboard stuff. I just hit mid 30s, and got my first mechanical board about 8 years ago.
In my 20s I modded cars too, to the extent that I had a mkiv supra that ran consistent 10s at the track. It had a stock exterior. All the money was in the motor and drivetrain. I even used stock 17" rims because I needed to run drag radials to keep it from fishtailing if I floored it at 75mph. Did almost all the work myself. So that's kind of like DIY boards. Now I have a car that costs more, but it's not modded. So that's less tinkering now that I'm older, but more cash up front lol. Sort of the opposite of your example lol.
As for keyboards, I like keycaps. I want them all. So that seems more rice-rocket than sleeper, at odds with my car history.
I'm also into switches, however, which is more like working on a car's engine. I have some box royals and hako trues on the way to swap stems and springs, and am on the lookout for a slightly stronger spring for Jades that doesn't turn them into Navys.
But I only built my first custom board very recently. Soldering is still a slow process for me, so I don't feel bad about paying someone who is more efficient at it to do it for me. I have a couple more boards coming that I will build myself, but overall it's not how I want to spend a lot of my time. Accordingly, I have custom boards assembled by others with all weights of Zealios, box switches, gaterons, etc. to try out switches and learn what I prefer. Not expensive GB customs, mind you. I just want switches and keycaps. Unlike cars, I've never felt like spending much time working on boards (rather than using them) I guess.
So in the end I'd say I'm somewhat lazy in my old age, and keep the DIY part to a minimum even though I'm into nifty switches. I have a lot of money sunk into boards not because they are expensive customs, but because I need a lot of boards to have all the switches and display all the keycaps. The only buys I regret are Cherry switch boards that aren't Leopolds.