SteamRank is a website where users can look up information about players on Steam. They also make this information available through the SteamRank API. The API has a "profile" call, which retrieves most of the available information about a given Steam ID, and an "ageEstimate" call, which retrieves the estimated age of a given Steam ID in seconds.
Steam has built out a global network over the years to ensure low latency, QoS, and protection from DoS attacks. A recent Steamworks SDK update allows Steam partners to access Steam's internal network so that the partners can leverage the same infrastructure that has made Steam resilient.