SELECT max value for each group of values order by grouped by MYSQL 8.x
On MySQL 8.0 one solution is using ROW_NUMBER function in this way:
Notice I've used Grp instead of Group, because it's a reserved word.
SELECT
  Person,
  Grp,
  Age
FROM
  (SELECT
    Person, Grp, Age,
    ROW_NUMBER() OVER (PARTITION BY Grp ORDER BY Age DESC) Rn
  FROM
    Ppl) a
WHERE
  Rn = 1
ORDER BY
  Age DESC;



Person | Grp | Age
:----- | --: | --:
Lalo   |   3 |  50
Shawn  |   1 |  42
Laura  |   2 |  39


There is no way to get Julia instead of Lalo, unless you add another column to the ORDER BY clause.
db&lt;&gt;fiddle here