Exactly. The American economy, including any rich economy in the world, will lose its dynamism if the Steve Jobs, Bill Gates decide to take big risks when they reach 70.
Risk taking is a matter of knowledge. I see young guys trading with an analytical approach, API development, and less of a naive approach than their previous generation about the markets. They had access to the internet since they were born (almost) and took advantage of all the free knowledge out there while many are self-taught (including coding).
The OP assumes that the risk taker is a young trader who saved $25K, and goes "all in". That is reckless, and I agree it should be avoided. But, many do not think this way. In fact, many saw how their parents lost their life savings in 2008 and are very wary in their approach. In my opinion, the new generation is self-directed in everything. They are not all "To the Moon" coin traders. If there is an age that people should take risks, is precisely when they are young. To argue against that because of QQQs is not relevant.
Risk-taking evolves our mind, and part of falling on your face and recovering is what will lead to the new leaders and innovators of tomorrow. Look at all the innovation around us, it is all as a result of someone taking risks. If they waited to take the chance when they were 70, I would have a "faster horse" not a car.

