I always felt it's a good think for F1 driver to get his chance in F1 very early as long as the team is going to support him despite his early struggles. People often look at the issue with a question: "Is he experienced enough to perform at decent level imediately?".
Ok, we can think of an 18 years old driver who can drive in F1 or in FR3.5/GP2 for the next two years. People only consider aspect that the driver would have a stronger rookie year if he has spent those two years more in feeders series instead of being thrown to F1 immediately. It's true. But let's look at the other side of this. If we have two identical 18 years old drivers, and one of them goes straight into F1, and another spends two years in GP2, who you believe to be a better driver after those two years? I believe the first one will be, and I do have some evidence to back up my view.
I've made a summary of amount of wins scored to GPs participated and podiums scored to GPs participated in relation to the age of an F1 debut by F1 drivers who had their first F1 race after 01.01.2000.
This is what I get from it:
Forgive me for any possible mistakes (I can imagine that those who have some experience with maths or statistics could spot something I've done wrong) and the fact that I will not describe here every single detail of how I used the data (it's just an interesting detail, not a scientific resarch, so no point for me to spend many hours on it). I could have been wrong on some details, but I'm pretty much certain the final outcome I've got is about right and shows the general tendency.
And the general tendency is that driver who start in F1 younger, do better in long-term. You may think that it's due to that the most talented drivers get their chance earlier, and it's certainly part of the explanation, but not the complete one, I think. No one will be able to convince me that for example Sebastien Bourdais didn't have the talent to score a single podium in F1, but he didn't get his chance early enough and that's how it has ended up.
It's just a simple pattern- the younger man is, the quicker he learns- it's a law of nature. F1 offers much more in terms of learning than any other racing series, so drivers who get their chance early will have the best circumstances to learn at the time when they can learn the most and the quickest, and they tend to benefit in long term from it. If one gets his chance at the age of 25, he will never going to be that good compared to the one who got his chance at the age of 20, because his natural ability of learning has deteriotated since he was 20 and he didn't do the most of it by driving outside the series which offers the most stimulus to learn.
One may point out that not every driver who started young was successfull. And it's true. It's also about talent and if one doesn't have one, it will not help him that much. But one thing is for sure- there was verry little success with all those late debuts and there are only 4 drivers who have won the race in F1 in XXI century and started older than 23. Those are Webber, Montoya, Kovalainen and Maldonado. None of them has won more than 10 races or become a WDC.
I believe Sirotkin has enough talent to give him a try. He has been doing considerable job against older and more experienced drivers in any racing series he was competing in recently. Hardly anyone had big very results (like GP2 or FR3.5 title) at his age. Being well in upper half of the field in very strong FR3.5 grid or finishing 3rd overall in Auto GP being that young and inexperienced is a sign of significant talent, I believe.