You're all still capable of it.
* https://en.wikipedia.org/wiki/Leonhard_Euler
* https://www.youtube.com/watch?v=qtkX18dU2_U
I don't know if he had access to, or consumed, tea or coffee. He lost his eye sight due to a progressive illness and the more his vision declined the more productive he became. He is commonly considered the most accomplished mathematician in human history.
Is it proven that he didn’t consume tea or coffee? Both were available in his time. England had coffee houses in the 1600s. Ever heard of the East India Conpany? They traded tea.
Besides that, you really think humans didn’t have awareness of various stimulant drugs at that point?
Did you read his Wikipedia page? I mean, the guy never got married, he had time on his hands. His Wikipedia page also says that he prioritized work over his own well-being.