You can check out this thread that is quite similar to everything you’ve asked here to see previous answers: Gaining weight of a female Hognose
I’ll answer here as well:
It is absolutely mandatory if you care about the health of your animals long term and doing things ethically. The actual recommendation is 3 years & 250-300g, some folks wait even longer. Breeding a younger, smaller animal gives you a higher likelihood of complications like eggbinding, can lead to smaller clutches in the future, impact the growth of the female, and lead to a shorter overall lifespan.
No. She may not even be ready by the season after that. It’s always better to go slow and let them gain weight at their own pace, even if it takes longer to get to size.