STUPIDITY

I feel stupid! I am 45 and changed work departments in August. But, when a co-worker, after having explained something to me, and I either don't get it right away or I ask a question, they say, "It shouldn't be THAT hard", I really feel stupid. I know that these younger "kids" (22-35) are smarter than me and pick things up faster. But, I don't know what to say to them when they get frustrated with me to get them off my back.

This isn't the first time a coworker has treated me like an idiot. I have a hard enough time not beating myself up whenever I make a mistake or can't remember something. I don't need these kids joining in! What can I say or do to let them know that we all can't be "as smart as them"?!