IME; males bred young and to young female - say sibling, originally same size. When spawning is complete, the male tends to the eggs and fry and will fast or only eat a bit. But the female on the other hand will return to a sorority, a bigger tank with lots of food. Inevitably the male will stop growing while the female continues.
To avoid this, I usually keep the female in a small jar and intentionally reduce her growth. This is useful if I plan to breed offspring to mother - 4 month old offspring = the size of mom.
How much bigger is the female? If she's not that much bigger and the male can still embrace her, you can breed them. Sometimes I fast the female or feed her merely enough and make her thinner (bigger females) because many of my females are too fat even for a slightly bigger male. In such case I put the female in an old planted tub fed once every 1-2 days. They will survive on what ever live larvae are in the tub, but will be thinner in a week or two.