Hi..
The age shows different in information, by mistake, u guess!
To answer your question.
Mostly , myopia becomes stable by 18 to 21 years of age, minor changes are possible , but in most of the cases, major variations, we dont see.
Does not look like degenerative myopia, do not worry. Dont read too much on goggle also.
Just wear correct glasses...maintain lifestyle , nutrition, stress etc..
Next Steps
do regular checks..