Evolving to a mature hairline

I was told my a dermatologist that I was balding, but nothing has changed over time as I did nothing to treat it.

You have retained most of your juvenile hairline characteristics. That is not balding, but I suspect you are slowly developing a mature hairline.  This evolution, in your case, is irregular and asymmetrical, but eventually, within the next decade, possibly earlier, it will be a mature V-shaped hairline.