Warne was a fitness coach, yet he can't keep players fit. Worrying. Yes their age will be a factor, but so will his training methods. Is he over training?
I'm sure many of you will remember Paul McGrath? Yes he was an extreme case in a different era, but he maintained a basic level of fitness, sometimes not training from one week to the next, yet he turned out week after week and did a good job.
I suspect Warne would be best placed to go gently with the older players, once they are "fit enough". Then he may just keep them fit and energetic for longer - NML included.