Hmm. Well, I have friends working at a couple of different GEMS schools (World Academy, Wellington) and they are finding them both okay, though I think they'd both jump to a BSME school (like DC, JESS) if they had the chance due to the better pay & accomodation.
As far as I know, the bottom of the scale (ie newly qualified) is 9,500aed/month and the GEMS teachers I knew getting paid the most (ie in their late 40s, been teaching for 20+ years) were getting paid 14-15k/month. You definitely wouldn't be the oldest - lots and lots of teachers out here are in their 40s & have families etc. You'll be expected to work hard, everyone out here does, but you get to have great holidays/weekends away too....
If you did take a job with GEMS, your accommodation would probably be in Discovery Gardens or Motor City (neither of them are great), but rents have fallen lots lately so you could probably get a nicer place with the housing allowance. If you want an idea of what's around, take a look at www.dubizzle.com
for people renting apartments/selling second hand cars & furniture.
Utilities per month will cost you about 500aed (including the housing tax which has recently been made compulsory for every expat resident, ouch!) Petrol isn't as cheap as it once was, but still reasonable.
If you were both working, you could definitely save a fair bit - particularly if your lifestyles are modest and you don't go crazy at the bars here (drinks are 40dhs a pop!!!)