He's the same age as Rendon.
Goldschmidt isn't a lefty and is older.
Goldschmidt was 1 year older, last year, than Rizzo is right now. He was also a much better player, coming off a 3-year total of 15.4 WAR while Rizzo is looking at a 3-year total of 11 WAR.
But if you want to compare him to Rendon, Rendon is projected to be 1.5 WAR more valuable next season, and was just paid $35 million, so unless you think teams are valuing linear WAR between 4 win players and 5-6 win players at $3-4 million per win, Rizzo wouldn't get $30 million, or probably anywhere close, on a long-term deal.
I mean jeez, JD Martinez got 5/$110 coming off a 1.066 OPS season, heading into his age-30 season.