I absolutely agree that they should have been scrapped. They were an underdeveloped idea from the start that was even more poorly written. They distracted from the actual running plot of RWBY and derailed everything that was going on. What was really important was Cinder's plans that were literally never elaborated on, Roman's involvement with them, and really WHY Cinder was doing what she was doing. All that along side basic worldbuilding that needed to be done to flesh the world out properly, and giving Ruby her own plotline because she's the freaking main character. And if they wanted to do the tournament arc they seriously needed to spend at least most of the season on that and actually do it right instead of the abomination of an arc that we got which was nothing more than filler until they got all dark and serious with the plot. The Maidens plotline was nothing but a plot tumor that damaged season 3 heavily and then ended up destroying the show as it goes on because it's just stupid.
And the age limit thing sounds like BS they came up with after the fact because it was brought up that Glynda would have been the perfect fit because she's already involved in the Ozluminati. It would mean they wouldn't have to bring in a random teenager. Any limitation on age is something the show does not establish and doesn't count. And this is even contradicted later by Raven who's clearly middle aged yet has Maiden powers. Nothing about this was thought through.
We've literally seen Semblances that are more impressive than Maiden powers. If they're supposed to have elemental powers it needs to be cranked up way past 11. I'm talking about summoning hurricanes, creating monstrous blizzards in an instant, creating earthquakes level of power. But what we got was lame and makes the Maidens look so stupid it becomes ridiculous that anyone would want Maiden powers when the increase in powers is negligible. Seriously Cinder looked like she was already strong enough to beat a Maiden before she got any powers so what was the point of it? All it did was give her a huge weakness to Silver Eyes, which is another thing that's been barely touched on and very poorly explained. If they wanted the Maidens to be impressive they needed to be able to do something seriously crazy like warp time and space to justify all that hype. But what would Miles and Kerry be without their terrible ideas and wasted concepts?