If there is nobody to teach him, how would he ever know?
He doesn't have a sibling or parent to learn from that mummy is a person who gets given gifts.
He is used to you being an unending source of things (love, food, gifts, clean pants, attention etc..) who never really seems to have any sort of requirements, rather than as another human who should be intentionally on the receiving end of things.
Do you take him to buy a present for his grandparents or your siblings?
If you don't, it's probably never occurred to him anyone would think of giving you a gift as in his world 'kids get gifts'.
Just be ready to smile when you receive the picture of Optimus Prime dancing on the heap of his defeated enemies or whatever.
No matter how weird it is, I promise it will lift your heart he spent even one minute doing something to be nice to you.
I also try to give extra praise for things he's put more time & effort into, because I want him to get the good feeling I get from giving gifts that make people happy, as well as to feel it is a thing people who care about each other do.
I have a special box I keep my 'treasure' in, & my pictures spend a month or so on the fridge before being popped in the treasure box.
He feels like he gives me things that make me really happy.
Don't tell him you are disappointed because I honestly don't think he's done anything but be the boy he thinks you want him to be.
Do you have stories you could tell him about gifts you gave/made for your parents/grandparents on birthdays or for Christmas when you were a child (only if they had good outcomes!)?
How happy it made them & how good you felt knowing you'd made them feel like you cared about them enough to get them a present?
If he can't see it happening in front of him, you need to tell it to him in stories/appropriate settings.
You could perhaps edge into conversation that you are excited he is big enough now that he can get you a birthday present this coming year, so he doesn't know you wish he'd been doing it before.
Make it seem a natural thing now he's so big his age is in double figures or something.
Not bang on a lot, but when birthdays/other times you might get a gift like Mothers day come up sometimes act excited about your amazing surprise.
Then near your birthday/Easter/mothers day, you could take him to a shop, give him a tenner & say you'll meet him at whatever part of the shop when he's found you a gift so it can be a surprise.
You'll probably need to give him wrapping paper & sellotape.
Then, however bad it is (I gave my dad 2 chopping boards & a plastic saucepan strainer at around that age) when you unwrap it, you need to model delight at your amazing surprise even if it's Spiderman bubble bath & you only have a shower.
I wouldn't try to make him spend his own money on you to start with, as that seems more like taking it from him rather than him giving of his own free will.
That comes with time (I have a now grown up child who went through all these stages).
Don't encourage him to get you something expensive even if you can afford it - you aren't teaching him to replace love with expensive gifts, it's the thought behind gift giving that he needs to learn.
If Easter is the next one, give him the money to get you an egg (same deal as birthday) & tell him how much you'd love a card that he made you because you treasure his art.
You just keep reinforcing that pleasing people you care about by giving them a gift/card is one way (but not the only way) to show they are valued & he'll pick it up because he will like doing something that will make his mummy happy.
He knows he feels good when people remember his special days (like his birthday, Christmas etc..), he needs to learn that other people will feel good if he remembers their special days.
I personally don't encourage my son to send me a Valentine, I don't see it as a day that has anything to do with kids.
He won't grow up knowing which are the appropriate times to gift a girlfriend/boyfriend or wife/husband/partner either when he is an adult if he doesn't learn it as a child & get plenty of positive reinforcement when he does make/give gifts (although some blokes just never seem to get it) so it's a skill a future DIL/SIL will appreciate too.