Check protein content on the foods you feed Rob.
Mine have shown some good growth already, keep nitrates under 20 ppm ect.
I'm feeding mine the New Life Spectrum Growth formula until I can find somthing with higher than a 58% protein content or whatever it's at.
They also like to snag the algae waefers from my cory cats and run off with em'.
From what I'm told, it takes 3 years for them to reach full adult size and for males to really develope their streamers, at around 1.5-2 years you'll start to see breeding activity ect.
I just power feed the crap out of my fish 5 days of the week, finish it off with a good helping of live blood worm to flush their guts out and then starve them for 2 days to make sure they don't develope bloat/dropsy from the overfeeding.
If you've got the time to do water changes and keep the nitrates low it does a lot for growth rates - I used to get my discus fry from wrigglers to 4" or so in just under 3 months using this method - though I fed a home made beef heart mix.