how old is John?

[stablpuw]

When John is twice as old as he is now, he will be four times as old as he was six years ago. How old is John?

[crofter]

He's 12

[teacher1]

My name is John, and I'm 60 !

[crofter]

method (if you want it)

If his current age is X, then when he is twice as old his age will be 2X and six years ago it was (X-6).

We are told 2X = 4(X -6)

So X = 2(X - 6) or X = 2X - 12

Therefore 12 = 2X - X => X = 12