I use a couple of treadle feeders , great for keeping most of the wild birds and other vermin out of the food, Tripod type drfinkers as weel but also an open trough seem popular both easy to empty and clean,
As for age of birds , once a bird is heavy enough top work it , mine is adjustable , but be aware if set for too light a bird then 6 blackbirds or 2 crows will also open the flap !