Are 4 week training cycles suitable for the over 50s?

Thanks for the feedback folks. What’s everyone preferred method of monitoring fatigue? I see there is a workout called ‘LSCT Warmup’ which claims to measure freshness. Anyone use this? If using resting HR, is that first thing in the morning? I’m on TrainingPeaks, but their ‘fatigue’ measure takes no account of age / recovery rate, and rarely coincides with how I feel. Thanks