Replacing Retired Players

Apologies if this is a topic which has previously been brought up on here. Am I correct in understanding that when players retire, you will need to replace them with players purchased from the auction house?
The retired player will automatically get replaced by a substitute player post by post. In the case you've only 15players in your team, the retired player will get replaced by a 6 stars new player. Then you'll need to purchase a new one.
I'm assuming those players are 18 years old with randomised training and recover speeds?
hmm i think they have like 30years old. I allways have more than 22 players so i'm not sure about that.
They are 30 to prevent them from being worth as much in the ah. Some people would spend good rp to buy a 18 yo 6* player
If you have only got 15 players before retirement then you have got a problem given the impact of substitutions in the game. In the past it did occasionally generate younger 6* by continually dismissing the replacements but it was not very often. Not tried it in a long time so not sure if still the case.
Does this in essence result in crazy bidding wars for younger talent higher up the leagues? With the few generated youngsters going for silly prices for to desperate teams
Selling a young player in the top levels for over 100 000 RP is a daily occurrence...
And selling a 6* 30 year old can pull in between 400rp-5krp.