I asked a somewhat similar question several months ago and this is what my research turned up regarding hammocks that older than 9 mo can sleep in -
1. Happy Hangup - out of Australia, there are mothering site members who love them but they are pricey. Sorry in a rush or I'd look up the names of members who have them!
2. Kanoe - out of US.
3. Special delivery, out of US (Hawaii). They've got a baby and toddler size.
4. A perhaps? knock-off of the Amby - or at least knock-off looking, that has a specific toddler version, called maybe Tiny Sleeper? Or something similar? May have been recalled, as I've only seen them on Ebay/Craigslist.
5. Make your own - search the mothering site or do a google search and you'll see that there are several good tutorials out there. The finished hammock often looks similar to the Special Delivery ones. Finding a spring seems to be an issue, but Kanoe (and maybe some of the other sites too?) will sell just a spring to you. Otherwise it seems as though many people go to car repair shops/garages for them?
6. It seems as though some folks keep their kids in the Amby for longer than 9 mo, sometimes with an extra spring, sometimes not - seems to depend on the size of the kid and how claustrophobic the kid is.