Your little brother will get it at his own speed, not yours. Nobody sped you up either.

Impatience with a younger person is usually impatience borrowed from somewhere. You were given time you no longer remember receiving, and the pace you now consider normal was built out of years of being allowed to be slow. Watching someone struggle with what you find easy tells you about the distance you covered, not about them.

When you find yourself rushing someone in your family, drop to their speed for one task. Let the silence while they work stay unfilled. The help they need is time, and you are one of the few people in a position to give it.