It's probably not even a month, approx. 1 to 2 weeks. You can't judge him/her right now. Try to feed him 3 times a day but pls. control so that your water quality can maintain in longer time. In prof way, you can feed him more than 3 times a day but the bad thing is you have to change the water the next day, however this made your fry grow fast. The guppy can only be transfer to your main tank with the adult after 3 months (minimum).