Why hasn’t my 7 yr old Banksia Serra’s flowered yet

Question

All conditions for growing seem to be covered and the tree is about 20ft high

Answer 1

I don't see your location listed, but these aren't well suited for a humid, moist area. They also don't tolerate phosphorus, so be careful if you fertilize, which they don't really need. Was your tree grown from seed? If so, it can take 10 years to bloom. Incorrect pruning can cost the tree blooms. Check out its other growing conditions listed in this article:

https://www.gardeningknowhow.com/ornamental/flowers/banksia/how-to-grow-banksia-plants.htm

If those conditions have been met, it might be a good idea to check with a local nursery or extension service for more suggestions.