Children and grandchildren should never come to Yimen: it's not that you don't want to be reborn as your children and grandchildren.
Just for the palace: just because you or your child made a mistake in the reincarnation process and it was not completely solved.
Stay in your forties: he won't be born again until you are forty, and those mistakes have been solved.
It's amazing that you didn't have this grandson until you were over 40. You have a lot to do in the future, and you will be able to honor your ancestors and make extraordinary achievements.
If you want him to come earlier, read more Buddhist scriptures, do more good deeds and accumulate more merits, you can eliminate the punishment you have committed in advance, and he can naturally be reborn earlier.
Conclusion: I have a son, but he came late. It doesn't matter how good you are.
Be a good person and have a normal baby.