Hi again Michele! I'm not sure about what age they would be full grown. I'm guessing close to a year? Platies can reach up to two inches when full grown. I have two Bright orange w/black finnage(females) ones that our just huge!! I got them when they were already almost full size. Now I have a baby one just like them about 4-5 months old.(don't know how she survived my Angel tho!) VEry cute! Hope I helped. ~Nancy~