pull in one's horns
1. To reduce your boasts; calm down from a quarrel; back down on a promise.
He said he could beat any man there single-handed, but he pulled in his horns when Jack came forward.
2. To cut back from one's usual way of living; reduce spending or activities; save.
After the business failed, Father had to pull in his horns.
As one advances in years, it is prudent to pull in one's horns more and more as to physical activity.