Tall has a different scale depending on what is being described, such as a tall dog, or tall house, or tall mountain. Verse 28 explains that He would spend his whole life there.
Mankind is limited, therefore anything referring to mankind about 'for ever and ever' is limited.
Burning forever in the fire means that man burns until there is nothing left to burn. An unquenchable is one that cannot be put out by man, but eventually goes out on it's own. The 1988 forest fires in Yellowstone Park could be called unquenchable, because there was nothing any man or army could do to stop it. But the fires did eventually go out when unfavorable conditions occurred. Jude tells us that God destroyed Sodom and Gomorrah with eternal fire.