Graded and ungraded adjectives
Pattern 5: as ADJ as num/amount
The adjective follows as and is followed by a prepositional phrase which consists of as and a number or amount. This pattern occurs with adjectives indicating age, size, and level, and is used to emphasize that you are talking about a very low or high figure.
Polls suggest turnout may be as low as 60 per cent.
They have often learnt violent and anti-social behaviour as young as three or four.