Bottle brush plant
I have had a pink bottle brush plant for two years and it has never flowed don’t no why I have two red ones and both flower
There are different types and some need to be quite mature to start flowering. Some are bred to start flowering from young. Do you know which types you have?
Are you growing them in the ground or in containers? Sometimes, growing in containers can restrict their grow, and that slows their development. The soil should always be free draining neutral to acidic with like plenty of sun. They don't like chalky soils. Grown in heavy soil in semi-shade will stunt their growth too. Lack of warmth can also cause them to develop less flowers.
From my experience, Callistemon Rigidus need to get to a decent size to start flowering.