I wonder if LEGO is going to follow the same fate, to no longer be of interest to Roblox and Minecraft obsessed kids, to develop an increasingly elderly customer base, ending up with just retirees.

I don't think this is true at all. Our daughter played a lot with Duplo and then Lego from ~2-12. Overall, she must have collected thousands of Euros of Lego from birthday, Christmas, and Sinterklaas presents. When friends were over, they usually wanted to play with Lego.

Us older people who remember the days of Lego without franchises and a focus on your own creativity/imagination might be grumpy about modern Lego (though they have been good at making adult Lego sets as well). But Lego is still wildly successful because they found ways to connect with younger generations and the franchise-based Minecraft/DC Comics/Star Wars/Harry Potter/etc. Lego is exactly one of the ways they have managed to do this, along with Lego for specific focus groups (e.g. Lego Friends).