This function can be used to calculate age taking into account that the years differece between the current date and the date of burth doesn't always mean the Age!! You should take into account the months and days differences.
For most DBAs, normalization is an understood concept, a bread and butter bit of knowledge. However, it is not at all unusual to review a database design by a development group for an OLTP (OnLine Transaction Processing) environment and find that the schema chosen is anything but properly normalized. This article by Brian Kelley will give you the core knowledge to data model.