Does it lose the restrained effect? when going to petrifed

This spell just feels like a worse version of Hold Monster tbh. failing multiple con saves vs failing a wisdom save.

Why would you want to petrify a target giving them resistances, when you can paralyze a target so that you do double the dice with attacks?

I just don't get the value of this being a 6th level spell

Is there a specific statement, that a creature turned to stone, stops aging or is that rather an implicit assumption?

Quote from Alethalion >>

Does it lose the restrained effect? when going to petrifed

 Hard to say, but it also doesn't really matter because Petrified does all the same things Restrained does and more. In the weird edge case that someone applied a cure for Petrified to the targeted creature without ending the spell, I guess the target would probably still be Restrained (until the end of the spell or three successful saves).

My players recently used this spell very interestingly. They encountered a Rakshasa that they engaged in plenty of political intrigue with, but it escaped after it realized it would lose the battle against them; this was, of course, after it clawed one of the party members, cursing them. I amped up the potency of that curse so that it couldn't be easily cured, requiring the 5th level Greater Restoration instead of Remove Curse, for the purposes of sadistically stressing out my party. The party, exclusively comprised of Half-Casters and Multiclasses, couldn't muster up such a large spell, and so they sought out a Cleric or Priest that would have it, but realized that it was much too far away for the cursed party member to survive.

So y'know what they did? They used this spell to Petrify them, suspending the curse at the cost of a party member (I just let them make a new character that'd either leave or join the party as an NPC once they found the one that could cure them), who they diligently preserved until they were able to have the curse lifted. I was planning for it to be a super intense, exhausting experience where they just barely made it, literally seconds more and they totally would've died, but they just used a 3rd level spell and a minute of Concentration and casually side-stepped like 3 sessions of pain. I couldn't even be mad, I just did some character development stuff about how they won't be able to see their lost party member for a while, and guilt-tripped them just a little when they had too much fun to force a little urgency and emotional complexity into the scene. Everyone said they had fun with such a shake-up, and there was a big realization as to exactly how much that party member contributed to the team, how much everyone did for that matter. 

I feel like it says something about the players here that a lot of the speculation about uses for petrification boil down to either 'Sculpting practice meets taxidermy!' or 'Recreating the Carbonite Freezing scene from The Empire Strikes Back for fun and profit!' It's like a personality-gauging question, seeing what route someone's mind goes to first.

(Mine admittedly went to the 'Flesh to Stone + Stone Shape' combo, mostly because I'm working on the bag of tricks of a twisted Warlock patron, an ancient deity with an artist's flair -- remaking troublemakers into more pleasing shapes was right up their alley, though it's sounding like there's a rule I can't find that precludes that. I'll definitely keep the Stone Stasis trick in my back pocket, though, now that I know I'm not the only one who thought of it.)

Hear me out, this is one of the rare spell vs magical effect vulnerability examples:

"subjected to the petrified condition for the duration"

"Maintain your concentration on this spell for the entire possible duration, the creature is turned to stone until the effect is removed"

RAW this implies that the target is ONLY considered Petrified during the 1m concentrated duration, and after the duration is ended the target magically becomes a stone object. This target would no longer be considered a creature or valid target for the likes of Greater Restoration since Petrification is no longer a condition post concentration. However this implies that this magically created stone is vulnerable to the likes of the much more available Dispel Magic remedy instead. This would also imply that spells like Stone Shape would work on the target, but only after the full duration of Flesh to Stone effect (think True Polymorph's creature to object ability).

Other petrification sources, such as a Beholder eye ray or Basilisk gaze, state that after the failed saves the target is considered a creature that is Petrified until the condition is removed, specifically naming Greater Restoration to remedy.