Her parents left her at Elbaf at the age of 5 and she consumed/killed mother carmel at the age she just turned 6 years old. She received her first 50 million bounty at that very same age because the story said that the big mom pirates started with her and that guy who witness the whole thing (in the caption).
2-3 years later from then (which I assumed because it took luffy 2 years to get 500 milli bounty) is still going to be around the age of 8 or 9 years old. I don't think she was 12 years old with a 500 million, by then she should've assembled a legitimate crew by then.
The same concept and portrayal of strength is almost the same as weevil.
Then what would happen if Kaidou and Shanks come out with 2 billion bounty commanders? It's not far-fetch considering the fact that we went from Ace a 550 million to Jack/Dogtooth being 1 billion bounty. That's literally 500 million more.
5 or 6 years old doesn't matter that much. The point is however that at the time she received her 500m bounty, she was definitely several years older. It's hard to estimate how old now exactly as she was definitely not adult yet, but she certainly was not a toddler of 2 years old. And I really don't get why you drag Weevil into this as we know absolutely nothing about him, so you can't draw a parallel with here.
And why would you even assume they have 2 billion bounty commanders? Yes it's quite far-fetched, but above all completely baseless and non-sensical. Ace is not valid reference point as he was special. The bounties of Marco, Jose and Vista would be far more appropriated, but we don't know them. There's also a huge difference here as jumping from 500m to 1000m and from 1000m to 2000m are not the same as the higher a bounty becomes, the more difficult it is to increase it.
People also seem to forget that all the Yonkou are of equal strength. There are not 4 emperors because they all thought that was a nice number, but because they had no other option than to tolerate one another. It's a balance that came into being almost in a natural way. So that Shanks or Kaidou would have a subordinate that's in a completely different league than Dogtooth, is highly questionable. If that was the case, they wouldn't be stuck in a stalemate as someone that has a bounty of 2 billion should be able to take on multiple commanders at the same time.
I don't dare predict anything about Shanks as he has always been the odd one out, but in regards to Kaidou I assume that Jack is his 2nd strongest commander at best as from a narrative point of view it's more interesting to not immediately introduce the strongest commander from the start. But I'm going to predict that the latter bounty's will at best be around 1.1 billion, take a few millions more or less.