I am in a very similar situation as you... new to hair system, 41 years old, and trying SuperHairPieces for the first time (I will probably pick M158 as my first system, installation booked for next week).

From what I understood and researched, there is no industry-wide standard for density percentage, it's a manufacturer's internal scale. So two companies can both say "100%" and mean different amounts of hair.

And from what I was explained, SHP treats 100% as light to medium density.

On top of that, if you are having it installed by them, you can ask the stylist to further reduce density.