There is no single 'ideal' weight
Robinson (1983) and Miller (1983) are modern standards based on actuarial data. Devine (1974) is still used in drug dosing. Hamwi (1964) remains a classic clinical rule of thumb.
Newer research suggests slightly higher BMIs (22–27) are protective in adults over 65 — our age-adjusted figure accounts for this.
Frame size, muscle mass, ethnicity and fat distribution all matter. Treat the range as a guide, not a target.