My girls were around a year old when I homed them and had a wheel and a few cat/bird ball toys in their cage. They really didn't play and their wheel was really chewed up so much it was at risk of falling apart (the gasket was severely chewed and almost completely pulled out). Ollie was around 4 years old, but had a ton of toys, he seems to prefer forage toys and man caves (hiding areas/toys s/a Arc, treehouse and a hanging frog he brought with him.
I've placed ball pits/toy bins, many foraging toys and some reset toys, most of which I made myself, a few purchased. Floor toys s/a tree house and an arc (had other house, barn and castle used for out of cage play). Also I started with adding braided vines and bracelets. They have dozens of toys and I interchange them, move them around, and use them differently where I can.
I try to have play areas (platform areas) throughout the cage on all levels. The play areas have consisted of a solid surface tray on floor to a fake branch either laying or standing on the floor, a shelf and/or natural branch from mid-to-upper area of the cage, and/or corner hammock placed here or there, a hanging basket/bin on occasions are placed in there as well as at times a square hammock hanging from the roof. These are areas where they can take food or toys (usually located in or near the area) to and enjoy. I usually keep two wheels in there now, especially since I now have a trio and they are on different levels as well. I keep a fleece bridge under the cage mount wheel to prevent poo and pee from falling below to other toys and accessories, they seem to enjoy using this bridge as a landing spot.
At first my girls didn't really seem to play, other than using the wheel. But as time went on and I tried having different things available I've noticed that they must have learned to play. I feel they mostly are looking for food
These are some observations I've had over time:
They still love their wheels!
They examine everything, especially forage toys.
When ball/toy bins are placed higher in cage, I've noticed they like to toss them (contents) onto the floor, I now will usually leave the pom poms in those, but occasionally use the ping pong balls or fleece strips and/or straws (things that are not heavy and make less noise, lol). When placed on floor, they're less likely to toss things out, but it happens time to time. They sometimes will pull things out of reset toys, but they don't go crazy over it. They chew on plastics, leave the wheels alone now.
On rare occasions, I will find a bracelet, and once two bracelets in their pouch. They are very picky about bracelets as the only type I'll find in their pouch are the thin, softer plastic ones that have a texture to them.