My personal opinion:

I truly think the 15 year old is likely to have a more favorable position.

0.1 BTC in 2085 will purchase a much higher quality of living than someone with 100 BTC in 2025, despite both being the same age.

This also forgets the factor that the 15 year old has decades to get to 0.2 or 0.5 hopefully even 1 or 10.

Additionally, in the next 60 years we may be able to extend health-spans so far not only will the 15 year old have a higher standard of living for a longer portion of time but likely live a longer life.

The 15 year old will probably live 20-50 years longer than the current 75 year old and likely retire 30-40 years earlier than they did despite a 5x-10x higher lifestyle.

This ignores the fact if the 15 year old is into Bitcoin so young they almost certainly understand the preciousness of every single year.

The caveat: The 75 year old is guaranteed to be rich now while the 15 year old is not certain to be rich in the future.

The message: We all need constant reminders that money is a tool but -truly- it is not the measure of wealth... Only of purchasing power.