Hi A., my name is A. and I sell Rainbow Playsystems and if you are looking for a playset that will last a very long time, than you are going to want to go with a playset that is designed to last. Most playsets that you see at Toys R Us and Sams, even Home Depot, they are built with treated lumber and treated lumber does not last a long time. Rainbow playsets are built with all redwood and cedar, so they are made to be outside for many years.
As for the age a child stops playing on a playset is going to be the age they grow out of it. I have a playset in my store and I see several 10,11, and 12 year olds playing on it just like the younger ones, so I would recomend you buy a playset that is built for a little older than you child is now, so your child can grow into it.
The expense of playsets is quite high, but I want to let you know that the resale value of a Rainbow playset is also high. I have looked on ebay and a few other websites and I have found 5-10 year old playsets selling for about half of what they sell for new.
So, please do the research and I think you will find that if you put a little more money into the playset, you will be much happier 5 plus years down the road.
Sincerely,
A.