According to Romans 4, what could Abraham do when he was about a hundred years old?

Get Sarah pregnant

And being not weak in faith, he considered not his own body now dead, when he was about an hundred years old; neither yet the deadness of Sarah's womb.

He staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God;

And being fully persuaded that, what he had promised, he was able also to perform. Romans 4:19-21

But heck, Abraham, when he was even older, managed to father six more children with a new wife without any divine assistance (Gen 25:1-2)