An information processing apparatus discloses herein includes an acquiring unit and an estimating unit. The acquiring unit acquires a plurality of pieces of identity information including a keyword based on an operation performed by a user. The estimating unit estimates an age group of the user based on the plurality of pieces of identity information acquired by the acquiring unit.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. An information processing apparatus comprising: an acquiring unit that acquires a plurality of pieces of identity information including a keyword based on an operation performed by a user; and an estimating unit that estimates an age group of the user based on the plurality of pieces of identity information acquired by the acquiring unit. 2. The information processing apparatus according to claim 1, wherein the plurality of pieces of identity information includes at least one of identification information for identifying a content that is provided to the user based on a request transmitted by a terminal device operated by the user or a domain related to a server device that provides the content. 3. The information processing apparatus according to claim 1, wherein the estimating unit includes a converting unit that converts the plurality of pieces of identity information to respective fixed-length values with a same fixed length; and a feature vector generating unit that generates a feature vector in a certain number of dimensions corresponding to a possible range of the fixed-length values, and sets values of elements corresponding to the fixed-length values converted by the converting unit among elements of the feature vector to predetermined values, and the estimating unit estimates the age group of the user by using the feature vector generated by the feature vector generating unit. 4. The information processing apparatus according to claim 3, wherein the converting unit converts the plurality of pieces of identity information to the fixed-length values with the same fixed length by obtaining hash values by applying a same hash function to the plurality of pieces of identity information. 5. The information processing apparatus according to claim 3, wherein the acquiring unit acquires a plurality of the keywords, the converting unit converts the keywords to respective fixed-length values, and the feature vector generating unit sets values of elements corresponding to the fixed-length values based on the respective keywords in the feature vector to predetermined values. 6. The information processing apparatus according to claim 3, wherein the estimating unit calculates, for each of age groups, a probability that the age group corresponds to the age group of the user by using the feature vector generated by the feature vector generating unit, and estimates the age group of the user based on the calculated probabilities. 7. The information processing apparatus according to claim 6, wherein the estimating unit sets thresholds for the respective age groups, and estimates that the age group for which one of a difference and a ratio of the probabilities calculated for the respective age groups and the thresholds set for the respective age groups is the greatest corresponds to the age group of the user. 8. The information processing apparatus according to claim 7, wherein the information processing apparatus generates, from a database in which the age group of the user is associated with the plurality of pieces of identity information, evaluation data including a correct value of the age group of the user corresponding to the plurality of pieces of identity information, including the age group of the user that is estimated by the estimating unit based on the plurality of pieces of identity information acquired from the database, and including a ratio at which the estimated age group matches the age group provided as the correct value, and the estimating unit sets thresholds for the respective age groups such that the ratio at which the estimated age group matches the age group provided as the correct value becomes equal to or higher than a predetermined value. 9. An information processing method comprising: acquiring a plurality of pieces of identity information including a keyword based on an operation performed by a user; and estimating an age group of the user based on the plurality of pieces of identity information acquired at the acquiring. 10. A non-transitory computer readable storage medium having stored therein an information processing program that causes a computer to execute: acquiring a plurality of pieces of identity information including a keyword based on an operation performed by a user; and estimating an age group of the user based on the plurality of pieces of identity information acquired at the acquiring.