Mine were sown in late January, (potted on several times and stayed in the light box in the house until they were about 1 ft tall) and I also bought some plug plants, just to have a comparison. I have found the two I have in buckets, using tomato compost from Dalesfoot, are growing much better than the ones in the beds, and I have had one really good sized aubergine already, a few more growing. But I also had a couple that went mouldy just after pollination, a problem I have most years... I also only allow two shoots to develop - check out Charles Dowding, he has a video on his channel about growing aubergines.
If you haven't got flowers by now it is unlikely that they will fruit successfully - this is what happens quite often to me.