Oh, he's probably around 5 weeks old, and you should actually start introducing solid foods to him now if you haven't already...Have you ever Abundance-Weaned a baby parrot before? I only ask because it's extremely important that you allow him to Abundance-Wean himself completely, and that you don't at all "Force Wean" him, which tends to happen accidentally by people who have never allowed a baby parrot to Abundance-Wean themselves before...
If he's starting to reduce the amount of formula he's eating during each hand-feeding that's perfectly okay, but if that's the case then that is your signal that you need to replace that formula he's no longer eating with solid food...Millet Sprays are a fantastic way to start to wean Budgies, they love them and they are very easy for them to shell and eat. So I would definitely put a Millet Spray into his Brooder or the heated box you hopefully have him in and when it's totally bare put a new one in (He cannot be without any heat just yet, it will be another week or so before you should move him into his first Weaning or Starter Cage)...
You also need to start to introduce him to fresh Veggies right now...Be sure to chop them up into little bits, and he'll most-likely just pick at them and not actually eat much of them at first, but if you don't introduce fresh veggies and fruit to them now, they won't ever really enjoy them or eat them with any gusto...Go easy on the fresh Fruit, as it's full of sugar which turns into fat and is stored in their Liver, just like the fat from Nuts, Sunflower Seeds, Dried Corn, and all the other treats and junk food is...So he should mostly be given fresh Veggies and dark, leafy Greens at this point, every single day from this point forward, so that he learns to love them just as much as he loves the seed-mix or pellets that you are going to wean him onto...
After you see that he is regularly eating Millet Sprays with no issue (right along with the fresh Veggies and dark, leafy Greens), then it's time to give him his regular "staple" food, which should be an Avian Pellet made for Budgies (meaning it will be quite small)...I actually typically would wean my Budgies onto a food that was a mix of BOTH healthy, low-fat seeds AND Pellets. There are several brands who make this mix for Budgies, the most common ones being Kaytee Exact (only the Exact Kaytee seed and pellet mixes, not ever their Fiesta or any of their other food types, as the rest are all extremely fatty and unhealthy for them, especially the Fiesta blends, they are nothing but fat), Ecotrition makes a Budgie seed and pellet mix, Zupreem Smart Selects for Budgies is another seed and pellet mix...
So start giving him a small bowl of fresh Veggies and fresh dark, leafy Greens that are chopped-up very well into tiny pieces every day in the morning after you give him his first hand-feeding of formula each day, along with a small bowl of a seed and pellet mix. If you don't wean him onto pellets now, it's very difficult to get Budgies to want to eat them later in life. And then continue his hand-feedings at the same times that you have been giving them to him, and what should happen is that he is going to start to reduce the amount of formula he's going to eat during one hand-feeding, then during two, and eventually all of his hand-feedings will consist of a much smaller amount of formula, until finally HE decides to eliminate an entire hand-feeding...It's extremely important that you allow HIM TO DECIDE TO ELIMINATE AN ENTIRE HAND_FEEDING!!!! DON'T YOU EVER JUST SAY "WELL, HE PROBABLY WON'T EAT THIS HAND-FEEDING, SO I'M JUST NOT GOING TO OFFER IT TO HIM AT ALL."...THAT'S THE ABSOLUTE WORST THING YOU CAN DO!!!
That is called "Force-Weaning", and it simply means that the person hand-feeding and raising a baby bird during the weaning process makes the decisions as to when the baby bird is given less formula in each hand-feeding, and they also are the one who decides when an entire hand-feeding is eliminated. This results in all kinds of physical health problems, psychological health problems, and most of all it causes very severe Neurological issues that usually last the entire life of the bird, which is also typically shortened when they are Force-Weaned. So always OFFER him the hand-feeding at the normal times of the day, and if you present the formula to him and he refuses it, then offer it to him again, and then again...A good rule is that if the baby refuses a hand-feeding after offering it to him 3 times, then he is choosing to eliminate it...Then you always want to make sure that the baby has both fresh Veggies and Greens and a bowl of seeds and pellets at all times once they start eliminating entire hand-feedings...
As soon as all of his mature feathers come in, he needs to be moved to his Weaning/Starter Cage...This is also very important, as his Weaning/Starter Cage must contain multiple toys, each one a different type of toy, one that is meant for chewing on (wood toy), one meant for shredding (cardboard/paper/streamer toy), one meant for beaking and banging around (the cheap plastic bird toys that you can buy at any Petco or PetSmart are great for Budgies, they love them), etc. If you don't put a lot of different toys in a baby's Weaning/Starter Cage, they literally will not know what a toy is, and they literally won't know how to play with them! Also, make sure the Weaning/Starter Cage has a ladder, so he'll learn to climb ladders, a Swing, so he'll learn to use a Swing, and Budgies love Swings, and that it also has a couple different types of food and water bowls/containers, so that he learns how to eat and drink from more than just one type of container...Basically, the Weaning/Starter Cage is meant to teach him how to live inside of a cage, how to climb and swing and eat/drink from anything, and how to actually play with toys and entertain himself...We get quite a few people come here because their new baby birds don't know what toys are and don't know how to play with them, because their breeders didn't put anything at all in their first cages, they just put them in a cage with a perch and one food and water dish and that's it...So they don't know how to play with toys, how to swing on a swing, how to climb a ladder, etc. It's sad...
If you have any questions at all, please just ask. There is no such thing as a stupid question, especially when it comes to Abundance-Weaning and hand-raising a baby parrot...