how do you increase beauty without surgery?
Hormonal balance 350+ will slowly raise it up to 50. Lower balance values have lower caps.
If you have maxed out surgery skill and surgery upgrades, you can do one surgery for +20 without losing natural look. This will prevent any further hormone-based changes.
If beauty is already 80+ and health and (I think) trust are high enough, it will go up to 100 on its own.
So anyone can go up to 70, and those who started with 60+ can get a full 100.
If you enable the option "children grow as they age", every birthday until 18 (included) they have a high chance to get +10 beauty if below 60, or a smaller chance for +5 if above 60. This also requires some hormonal balance, I think 100+ for girls and 200+ for boys. This random roll is seeded and impossible to save-scum.
If someone starts early or beautiful enough, you could eventually get them to 60, surgery for 80, and automatic to 100... if you wait for years and get lucky rolls.