This is a nonsensical argument you keep making. Why is age more important than experience? Robles has now had seven seasons of professional ball: four minor league seasons and three in the majors. He shows no sign of being able to hit major league pitching. His fielding is OK, but no team starts a .200 hitting CF with a .600 OPS just because they field decently.
"Robles is only 24"??? So what? What shows he is learning to hit? That he raised his average all the way from .195 to .205?
If July was a time to be realistic about the organization and the 26 man ML roster, what justifies Robles taking a spot?
Age largely equals experience, at least in total number of at bats. Robles has a lot of major league experience (and overall pro experience) for someone who's 24, which is not surprising as he was playing professionally since most US-born players would still have been in high school. Keep in mind, Robles is about 3 months older than Carter Kieboom.
But. There's a but. And that's that most guys his age have a lot of pro at bats...just all in the minors. For example, you can still compare him to someone like Andrew Stevenson, who was playing regularly in the SEC - a higher level than Rookie ball - at age 19. They were teammates several times on the way up, and Robles was better - despite being three years younger. He also turned into a better player at the major league level. Stevenson actually had some success in small samples at age 25 and 26 despite being terrible in MLB prior to that.
And why this matters is that at 24, you still have some room for improvement: position players typically peak at 27-29, which is what Stevenson is. You can also compare Robles to Cedric Mullins, who after his age-24 season was a career .197 hitter in the majors with no power. At 26, he's hitting over .300 with 21 homers while playing CF and deservedly making an All-Star team. Or Bryan Reynolds, who opened his age-24 season with zero major league at bats and now is 26...also hitting over .300 with 21 homers and an All-Star. Randy Arozarena: 20 MLB at bats at age 24. Now at 26 is at .275 with a bunch of power and a ton of walks, hitting at the top of the order for one of the best teams in the league.
And that's just the age progression for three guys who were nobodies in MLB terms at 24 and now are stars right now at 26. Who knows if Robles follows that path, but the unusual for him is he was up and successful at 22, not that he's stinking in MLB at 24. And as for guys who were awesome at 22 and then struggled later for a bit, at least in relative terms, try Bryce Harper: he was Babe Ruth at age 22 and then...well, not so much at 24 and 25. Now he's excellent again.