Is it too much to ask a 23 months old to wait for his turn to play with the swing at the playground? Or they are still too young to understand that ?

It's good to let them learn to wait for a certain time. Meanwhile, explain to them that we need to wait for our turn while other children are still playing, we can play at other games or queue up for the swing. But of cos I understood same kids just will never let go the swing, so by all means we can left & redirect yr child that next time we can come again.