Their youthfulness

Appleby tells us that by the mid-17th Century the average clergyman began ministering in his mid-twenties and commonly went on for another 30 years. Seaver says that in 1640-1662 the average age of incumbents rose to 42. Appleby says that the average age at the Ejection of those listed in Calamy Revisited (where the data is available) was 41.9. The average from those who published farewell sermons is 39.6. Ten Midlands authors featured in England's Remembrancer were on average as low as 32.7. The point then is that far from being past their prime, those ejected in 1662 were younger than average.
Even the older ones could be very energetic. Appleby cites Richard Fairclough (41) who habitually rose at 3 am to squeeze in all the various things he did in a week. This factor should be borne in mind when we consider how it was that these men (unlike the elderly bishops recently restored) went on preaching for decades after 1662.