after 6 months they are considered adults. but if they are growing out in a smaller tank then they might be smaller than the ones you have in a larger tank. some guppies are just smaller than others. my endlers are much smaller than my others. and i ahve a 1/2 black one who is some what small compaired to my lyre tail and 1/2 yellow one.
10 gallon tank guppy and platy fry, pleco
20 gallon female gups and fry.
25 gallon male gups
55 gallon 1 neon tetra,1 algae eater, 6 glow lite tetra, 1 long fin zebra danio, 3 long fin golden danios, 3 purple danios, 3 longfin blue danios, 1 rummy nose, 1 lyretail neon swords, 1 dwarf platy, 2 cherry barbs, 1 gold barb, 2 blood fin tetra, 2 red eye tetra, 1 pleco, 2 glass fish, 2 spotted picus cat, 2 green cory,