Can you not notice you have degenerative myopia?

I read in this blog: https://www.kcretina.com/blog/about-degenerative-myopia-and-your-options-for-treatment

That some people get diagnosed in their 30s or 40s, is that for real? I thought I was in the clear 🙁 I'm 20 and my -6.5 has been stable for 2 years but now I'm anxious it might keep progressing at some point. Can anyone please let me know how does this work?

Also, just so I don't get banned for spam I'll ask this in here as well, I'm on my computer a lot of school and my phone on my free time, will that make my myopia progress, I'm kind of scared about it. Thanks in advance