I clicked over to the Albums section here on the site and read the lyrics. What I believe it's about is how he looks back on a relationship he started with some woman,when he was younger. The line about "having you on my knee" could be one of his youngest kids I'd guess,or the woman herself. It seems to be written in past tense so I guess maybe it's not the relationship it started out to be or else he's taken aback by how long they've been together.
I'm sure there's more ways to look at it but that what I get out of it. Later!
------------------
Borderstone,gonna post some lines tonight!:D