How old is too old for an allowance?

Chebbar and I had to have a little chat this past weekend.

You see, he has dropped the phrase "We need to get back on track with our finances" three times since the beginning of the month.  Now, I am the one who handles our finances: I have handled my finances to the point that I was able to buy my first home on my own; he asked me to help him because he's not so good at managing his money.  He is the impulse spender; I'm the one who agonizes over spending $30 on a purse for so long that he ends up going and buying it for me.  He spends money with little thought, albeit likely because I've made it easy for him to do so by taking care of the bills.

The first time he made the finance comment, I winced a little, but conceded that it was likely a fair observation -- we *had* gotten away from our goal(s).  The second time he made the statement, I bristled because, as I said above, he's the one who will drop $23 on renting video games, blithely inform me that he "forgot" to cancel his Xbox Live account (that he's been talking about cancelling for WEEKS) which resulted in a $60 charge to the credit card, then turns around and talks about renewing his WoW membership at a cost of $80 for six months.

The proverbial straw was me mentioning that Blue Rodeo would be playing close by and tickets were CHEAP.  He looked at me, brow furrowed, and issued that blasted sentence a third time.  My reaction, in my inside (my head) voice?  Screw you, too, hypocrite!

I did bring it up briefly, but we were on our way to my parents' house, so the conversation was short-lived, leaving me feeling burdened.  We ended up using Gail Vaz-Oxlade's -- of Til Debt Do Us Part fame -- budget tool to hammer out where to put our money.  Included in the budget sheet was a box for allowances.  Now, I'm guessing this intended for parents to work their children's allowance(s) into the family budget.  However, after talking to my mom briefly the night before, I was inspired to make that work for us.  I proposed an allowance of $100 a month for each of us to do with as we wish -- if he wants to renew his WoW subscription, he can go for it; if I want to save up for that Clarisonic face brush (KILL ME WITH WANT -- thanks, Loralee *wink*), that's cool.  The understanding is that neither one of us will question or criticize what the other chooses to do with his or her allowance.  As well, once it's gone, it's gone and we're SOL until the next month.  Chebbar had the good idea to withdraw the cash at the beginning of the month to put in separate envelopes so we're aware of how much we've spent/have left. 

The only thing we haven't nailed down yet is the difference between necessity and non-essential items.  In my oh so humble opinion, if we need underwear or something for work, those are necessary items that should come from the communal pot.  On the other hand, if he wants a new video game or I want a new purse, those are non-essential items that should come from our allowances. 

Has anyone else used this type of setup?  What worked for you?  What didn't?  What did you do about essential items?  Did you call it an allowance, or were you able to come up with a term that was less... 6-year old doing chores?