I think you've missed the point - it feels odd given that we've "known" her since she was a girl. No-one is arguing about her being of age now, just if feels a bit uncomfortable watching.
It's a bit like rocking up at a strip joint and finding your neighbours 18 year daughter, whom you have known all her life, is working there. It's not illegal, but it feels very wrong.
I've got to say I enjoyed this episode as much as any other I've seen. I don't understand the complaints about a lack progression, it felt like the calm before the storm, old adversaries and friends preparing in the lull before an epic battle. Just because the main plot didn't take a step forward doesn't mean that the story didn't progress, there were a shed load of side plots that were partially wrapped up in that episode, we got to see what had become of a number of secondary characters who aren't important to the plot but are important to the experience (Pod, Gilly, Mini-Mormont to name a few). On top of that there was unfinished business between characters that we needed closure on, Arya and the Hound, Sansa and Theon, Jaime and pretty much everyone. One of the most difficult parts of writing a saga like this is apparently how you get everyone to where they need to be by the end of the story, I feel like GoT handled it pretty well in this episode and at the same time offered some nice closure and throwbacks for fans.
In terms of major character deaths it'll be interesting to see what happens, my thoughts below:
Dany - I would have said safe during the battle of Winterfell but the Jon reveal means she's potentially superfluous. Would be a ballsy move to kill her before episode 6.
Theon - Dead, so dead, very very dead. His arc surely can't be anything other than redemption through heroic sacrifice? Though I would be amused to see him scarper once more never to be heard from again.
The Brotherhood - Dondarrion can't keep it up for ever, could go down protecting the hound.
The Hound - This is an interesting one, book fans would be ****** if he didn't get to face down his brother, but the show didn't push his backstory as much as the books did.
Jaime - Symmetry insists he lives to kill Cersie shirley?
Brienne - Loads of people predicting her death, I would like to see her survive, she was handed the mantle of Knighthood by Jaime, he represents everything she's ever wanted to be, but she represents everything he could have been. Could go either way.
I reckon Sansa or Dany will go, clears up that nasty civil war situation that's brewing too.