I have no experience with lovies other then peachies, but when Fëanor came here he was about 8 months old. He weighed a bit over 40 grams and was a good bit smaller then Henkie(60 grams). Now he is somewhere around 1,5 years old and weighs 58/59 grams... I think his weight gain had a lot to do with muscle and normal weight gain, but he has also grown in size as he is now as big as Henkie? I don’t know to what age they normally grow in size. Maybe it had to do with his improved diet.
https://www.parrots.org/encyclopedia/masked-lovebird
According to that website personatas weigh between 43 and 50 grams, could be he is just a Tiny boy!