My muscles remain the same size even if I dont train

[Mike456]

So I started the gym again after some months and I noticed that my muscle mass doesn't change. Even before I didn't go to the gym my muscles remained the same size.
Even before started working out I had above average biceps(like 9 years old). An summer I helped my dad with stuff and I got bigger biceps. Since then my biceps haven't shrunk only grew.
Is this some sort of gene mutation or some shit. Everyone says that if they stop going to the gym they lose muscles.

 

[Sujumh]

Muscle Memory and Myonuclei​

When you grow muscle, your muscle fibers add nuclei (called myonuclei) to support growth.
These myonuclei remain even when you stop training for months or years.
When you return to training, your body rebuilds lost muscle size faster, or even maintains muscle better than average.
also when ur a beginner u build muscle doing jackshit btw this is js chatgpt