Both ... I guess.
If they reach 3cm (BO) by 4 months, I breed them (regular bettas).

But for giants, it's safer to wait until they reach 6cm (BO) because then you will be positively sure that you will have true giant fry.
I bred a 4cm female (The blue), now the fry look so tiny.

Most People in my area will advise 5+ months, believing that at that age bettas are more genetically stable and will produce better eggs and fry. This is at least 60% true. But young bettas will spawn and can produce strong fry. But not as many as older bettas (less than 100).

I with you on that....
When a fish just go without a know cause.
It's puzzling....

Hey from your point of view.
Do you breed in size or age.
Was thinking about breeding my babies giants in two week.
They should be a little over three month.

I hate when that happens. I mean at least give some sort of warning that they're going to go.... lol.
Even adults often do that - they suddenly die without showing me why. I humor myself and just think that it's some sort of fish pneumonia because they're constantly wet during bad weather ... lol

I didn't start recoding my giant until they hit 9 week old.
But that seem right.
My giant didn't explode in size until they hit the fifth week.
That's is kind of dispersing.
I have the same problem with my big earxdt.
One week I have over 100 and the next I drop down to 7.
Don't see any dead bodies

Yeah it's been a while - was kinda busy.
No, I haven't got any new fry.
Anxious to see the outcome of the blue giant spawn.... they're so tiny at 4 weeks (for giants - only about 6-7mm).

Odd thing is that the green giant spawn that I thought was better than the blue, almost died out (kind of disappeared) for no apparent reason (only 2 left).

Long no talk.
Any new breeding...
Yeah I just pick up two male hm giant which I'm going to cross them to my babies hmpk giant spawn.
The babies are growing at a good rate.
Almost three month and the biggest one is about 2.5in