It depends entirely on what that request is and how interesting it is.
My 9 year old has ADHD. He can remember little tidbits of information I only gave him once, 5 years ago, just because they somehow interested him, but not the rules about laundry. He has to ask EVERY SINGLE DAY confirmation from me about how to sort his laundry. For goodness's sake!
No elbows on the table took him a year, at the rate of at least one reminder per day. He's got that now.
Then there are rules that play directly into his OCD tendencies, like washing his hands after going on the toilet, before dinner, or when coming back from school - I'm not even sure if I ever told him, but he does it anyway, religiously.
This is the secret my SIL told me. Parenting is hard because you have to be a cop all the times, 24/7.