One important thing that article failed to mention is that the cohort studied had been highly physically active most of their adult life. The study didnt show that exercising at the age of 80 gives you the thymic fitness of a 20 year old, it showed that if you exercise vigorously for 60 years your thymus will still be fit at the end.
Exercise was not shown to reverse thymic involution, just to slow or even stop it.
So dont wait, exercise now.
I would love to see clinical studies on harmine treatment or protracted fasting on thymic function in the elderly. Both have been shown to have a regenerative effect on other organs.