genetics? maybe something early in life just set the timer off and it flowered earlier than others? It's still got some vege growth left, it looks.. so it may bush out more befoe it's done.
more perlite or similar for drainage may help. vermiculite adds plant useable silica. with soil it's better to be near 50/50 with perlite or equivalent. if this was somethin within your control, an improved root zone would help. you'll need to irrigate more frequently, but better aeration and general health for roots. studies show 50/50 is best with a substrate that holds a lot of water... this is why coco suggests 70/30.. it holds 2/3rds the capacity of typical 'soil.' (which is a loose/boad categorization in itself) so, if it's lighter than typical soil, less than 50% is good too, and in genral 50/50 doesn't ahve to be super precise of course, lol... small potatoes within eyeballing-it range of error.