A bio-information estimating apparatus (100a; 100b), comprising: a sensor part comprising: a pulse wave sensor comprising a light source configured to emit light of multiple wavelengths onto the object, and a detector configured to detect light scattered or reflected from the object, the pulse wave sensor being configured to measure the multi-wavelength pulse wave signal at a first point in time when a first pressure is applied from an object to the sensor part and at a second point in time when a second pressure is applied from the object to the sensor part, wherein the multi-wavelength pulse wave signal comprises a first pulse wave signal of a first wavelength and a second pulse wave signal of a second wavelength, wherein the first wavelength is shorter than the second wavelength; an area sensor configured to measure a contact area between the object and the pulse wave sensor; a force sensor configured to measure an intensity of force applied by the object when the object touches the area sensor; and a processor configured to: obtain contact pressure based on the intensity of the force and the contact area, calculate a ratio between an intensity of the first pulse wave signal and an intensity of the second pulse wave signal for each of the first and the second pressures, obtain a first value and a second value by applying a predefined function to each of the calculated ratios, respectively, wherein the predefined function comprises a logarithmic function, calculate a difference Δf between the first value and the second value, and estimate bio-information by applying a bio-information estimation model to the calculated difference, the bio-information estimation model representing a correlation between the calculated difference Δf and a degree of skin tissue aging or a biological age of the object. a pulse wave sensor comprising a light source configured to emit light of multiple wavelengths onto the object, and a detector configured to detect light scattered or reflected from the object, the pulse wave sensor being configured to measure the multi-wavelength pulse wave signal at a first point in time when a first pressure is applied from an object to the sensor part and at a second point in time when a second pressure is applied from the object to the sensor part, wherein the multi-wavelength pulse wave signal comprises a first pulse wave signal of a first wavelength and a second pulse wave signal of a second wavelength, wherein the first wavelength is shorter than the second wavelength; an area sensor configured to measure a contact area between the object and the pulse wave sensor; a force sensor configured to measure an intensity of force applied by the object when the object touches the area sensor; and a processor configured to: obtain contact pressure based on the intensity of the force and the contact area, calculate a ratio between an intensity of the first pulse wave signal and an intensity of the second pulse wave signal for each of the first and the second pressures, obtain a first value and a second value by applying a predefined function to each of the calculated ratios, respectively, wherein the predefined function comprises a logarithmic function, calculate a difference Δf between the first value and the second value, and estimate bio-information by applying a bio-information estimation model to the calculated difference, the bio-information estimation model representing a correlation between the calculated difference Δf and a degree of skin tissue aging or a biological age of the object. obtain contact pressure based on the intensity of the force and the contact area, calculate a ratio between an intensity of the first pulse wave signal and an intensity of the second pulse wave signal for each of the first and the second pressures, obtain a first value and a second value by applying a predefined function to each of the calculated ratios, respectively, wherein the predefined function comprises a logarithmic function, calculate a difference Δf between the first value and the second value, and estimate bio-information by applying a bio-information estimation model to the calculated difference, the bio-information estimation model representing a correlation between the calculated difference Δf and a degree of skin tissue aging or a biological age of the object.