When and how often is it the newbies' turn at the keyboard?
And as the senior feels slowed down, how can he then cope with impatience?
I think it's often hard to tell. One way of addressing this problem is to eliminate the friction associated with switching roles.
We always pair with two keyboards, two mice, and two monitors plugged into the same machine. There's just too much friction associated with switching spots if you only have one keyboard.
If you don't have the equipment for that setup, you can set up a virtual pairing station with ssh and tmux pretty easily.
so basically both are fiddling around with the same cursor?
But yeah, 2 keyboards are a necessity
The senior should assume he will be slowed down (if working with a noob). This is just a matter of how much patience the senior has. One easy solution is to take breaks.
Another thing to mention is that we generally rotate pairs fairly regularly. A developer will work with others with very different levels of experience both in general and within Braintree.