Drogon is still to small compared to Balerion the black dread.

[Mad Titan Thanos]

Drogon is still too small compared to Balerion the black dread.

I am re-reading my books so I notice how huge Balerion was. I was thinking Drogon is already his size but I was so wrong.

Balerion the black dread was the biggest dragon.His wingspan so vast that entire towns would fall under his shadow.

His jaws were large enough to swallow an aurochs whole, or even one of the hairy mammoths.

So he can swallow a mammoth . We know how huge mammoth is its Giants ride them.

Look at size of mammoth

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Imagine head that can swallow it.

Now look at Drogon head size.

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So as wee see Drogon still has a lot to grow.

 

[Caliburn]

Well yeah he's barely a few years old while dragons can live for centuries. They also never stop growing, similar to snakes in real life. If Drogon had already been as dreadful as Balerion, Dany wouldn't be in the situation she's in now.

 

[Mori Jin]

1 of the writers for the series was quoted saying, that in season 6 drogon will be 120 feet from the the end of 1 wing to the other/ from head to the end of his tail.