Nina is a year younger than me and she's cool, but Ricky is six going on two. He is a total pest, and Mom and Aunt Lucia are always asking us to watch him.
Does this underlined part mean,
Ricky is six, but he is acting like a two years old baby?
Please help! Thank you.
Well done! There's also an expression that uses the numbers the other way round: 'She's 11 going on 18'.
Another saying that relates more to your image:
'Men are like boys; it's just that as they grow up their toys get more expensive.'
(I just pass this on as a point of information - though I have to admit that it has a kernel of truth. )