Wow, this thread is quite united and with lots of helpful comments for the OP.
For the record, I faced a similar situation a couple of years ago in considering a grandkids' gun. I ended up getting a Kimber Hunter (similar in price to a Tikka) because of its extreme light weight. Someone 9-10 or even 12 or older enjoys the lightness of the Kimber. That said, I think that the Tikka is an EXCELLENT choice for a first rifle. They, too, are light, and every Tikka that I have owned have been shooters right out of the box, although I have "mini-bedded" three of them. Your son will know that you love him.
Caliber raises a second question. I, too, will side with those suggesting the lighter caliber(s), although my own choice for a grandkids' rifle was 308. The 308 is a better caliber where larger game are expected, and I plan to host grandkids in Tanzania after this Corona thing finishes. Hartebeest and cow elk can benefit from a larger bore. But for deer, reedbuck and impala, the 6.5 CM would be great, as would the Bob, the 257Roberts.
There is a special consideration for not choosing a 308 if you go with a Tikka3x. The Tikka 3x uses an 11" twist in its 308. Admittedly, that twist is adequate for light to medium bullets and a young hunter is probably going to be hunting deer where the light to medium bullets are more than adequate. However, some of the special long-range bullets may not work as well as in a rifle with 10" like the Kimber and many others. This is an important characteristic for choosing a caliber. Manufacturers of 308s split into three camps, those with 10" twist, 11" twist, and 12" twist. In these days of copper bullets and long-range bullets, the faster twist is strongly recommended. So if a Tikka 3x is chosen, then the caliber should probably be 6.5CM, 708, 260, 257Bob, or even a 243. They are all excellent. (PS: the Tikka uses the same action for 270 or 260, there is no "short-action" model for the 6.5, 260, or 243. That also allows Tikka to produce a 257 Bob and the 270 Win in the exact same model and action.) These days the 6.5 is considered sexy, so go with that for your son and explain what that means after he gets his first deer.