Welcome and happy birthday!
I agree your adorable tortoise has probably been kept too dry; you can see how his shell looks a little bumpy, even for a Russian.
Can you show us some pictures of your enclosure? It may be that he was kept too dry at the breeder’s and you’ve adjusted his care by now but we should check to be sure.
Aspen won’t hurt him right off but it’s fairly dry. Fine grade orchid bark, perhaps mixed with some coco coir, is best; you can buy both cheaply at a nursery
Don’t over do with the calcium dust, it throws off the taste and they don’t need too much at that age. The tiniest sprinkle, perhaps two or three times a week. Toss in a small bit of cuttle bone and he’ll eat it as he feels the need. Get the kind sold for birds, they’re the cheapest.
Do you know what he was eating at the pet shop? Even if it wasn’t ideal you can sometimes mix a bit of the new food with the old, until he gets used to the new food. Over time you reduce the amount of the old food. If you can’t, don’t worry about; he may be too nervous to eat until he settles down in his final enclosure.
Looking forward to pictures!
That’s good. You can moisten the food and chop it up a bit with the other foods; it will help him get the taste of it.
I’m not an expert on lighting (my tortoise lives outdoors) and someone smarter than I am will give you feedback on it. What I can do is ask if you bought that setup at the pet store, it looks like a pretty common one. I’m afraid they are much too small. Russians should have a minimum of eight by four feet (we can help you build a two story if you don’t have that much floor space). If it’s not too late to return it, you should think about it. (I’m sorry to say this, I know it’s hard to hear.)
I think you’ll also want a way to increase the humidity on top of the soaks, which you just can’t do in the covered/hiding side of the box. If you’ve not already read them, please take a look at our care sheets. This one is for babies:https://tortoiseforum.org/threads/b...or-other-herbivorous-tortoise-species.107734/ and this one is for adults: https://tortoiseforum.org/threads/russian-tortoise-care-sheet.80698/. Your tort is somewhere in between but babies and juveniles need more humidity. This is another area where you should get additional, smarter advice as I’ve only ever had an adult tortoise.
Also the bowl is not good for tortoises; they can’t bend their heads to drink so can’t really use it. A better choice is a cheap terracotta plant saucer a little bigger than the tortoise. If you can’t manage that, see if you can find a way to get the top level with the substrate (dig it down). It’s another item that you should return if you still can.
I know this may come as a shock when you’ve clearly tried to do all the right things for the setup. Pet stores don’t usually know much about tortoises and they are in the business of sales. Just about everyone here has bought the wrong things at the beginning.