their colors dull. for example, instead of bright purples and blues, they would be a dull lavender or baby blue.
the size of it's fins and body
Adult betta fish, specifically the males, will grow in the majority of their fins as juveniles. When you see bettas in the stores for sale, they are typically around 2 years old already since it takes time for their full finnage to appear.
A betta normally only lives 2-3 years, so it would be around 70 years old in "betta years".
Betta fish grow paler and less active when they are sick or old.
A nine month old betta is already full grown, so yes.
'I'm not 2 sure !
They can live up to 3 years.
To the best of my knowledge no one keep those kind of records. Bettas are mature at 12 months, past their prime at 2 years old and ancient fish at 4 if they live that long. I have a Betta fish that is now over 5 years old because I change the water once a week with 2 gallons of purified water and I add about 20 drops of Splendid Betta Complete Water Conditioner to it. Using the water conditioner is a MUST to ensure that your Betta fish will live a very long life. I also feed my Betta fish 4 pellets of Hikari Betta Bio Gold once a day in the morning and 1 pellet at around 7pm.
No one knows. There have been no records kept.
3-4 months.
This maybe is because old rotted food is in your bettas water.
Most likely. I would wait until the little betta is around 3 cm (3/4 inch) Make sure the betta's are the different sex because two males will fight (often until death)