Our aubergines are now about two feet high and the purple flowers are just opening now in the polytunnel. Outside they are further behind.
Concentrate on growing the plant to a good size as then it will be able to bear better and larger fruit. The actual aubergine doesn't take long to form once the flowers are open, and as you pick them before they are ripe, at an immature stage, I wouldn't worry about not having any flowers open yet.
Aubergines taste better when picked when relatively young and shiny, and if you leave them until the skin is dull and they are too big, the flavour will be much poorer. The more you pick, the more fruit will form.