When does a blackthorn flower?

Mr N sent us a question: I bought some blackthorn specimens from yourselves in 2009 to create a
defensive planting.   Although the plants are growing well and seem
healthy, they have still never flowered.  Someone suggested that they
might not be female specimens.  Is this suggestion a load of rubbish
or is this species one of these plants with male and female attributes?

And the answer is:
The blackthorn flowers are hermaphrodite (have both male and female organs) and are pollinated by Insects. They should flower when around 5-6yrs old.