I don't think it's that long. He's 21 now. So he'd be 24 when he comes back. That's still young, especially for a heavyweight. I can't think of any heavyweight who was medalist level at 21 (like he is now) and then wasn't in his mid 20s, barring extreme injuries.
Gable wasn't training full time and we don't really know if he could have won a medal since he never committed to being a world teamer again. He crushed Mason Parris the same year that Mason who won a Bronze medal at worlds, so evidence points to him being world level medal, but choosing not to participate. Masoumi will presumably be training FS full time during his 3 year hiatus, I'd think.
What's the alternative, trying to age out Zare who is in his mid 20s? That might take forever and rob Masoumi of a career. No one is going to care about your loyalty when you're in your late 30s and have no world level medals to show for it. The nice jobs and perks will go to people like Zare, who have medals.