A weight would help too but its all just a estimate. At 3 months mine was only 78 grams and 18". She was very slim.. She is 300 grams as of yesterday and had a mouse sense her Poo .. I
Id say you were closer to 4 mos but who knows. Just make a age from now on and go by it. I could be off too as its only the age I was told when i bought them.