DESC: Within a population a child must mature, before they can take up a class or be recruited into service as a unit. The racial levels reflects a continued development after a individual reaches that mark.
These levels will force a restricted class selection on the individual to those classes titled with racial. This also reduces the number of class levels available. If you take 20 racial level, then you will only have 80 class levels to advance in. A race that takes all 100 racial levels can not have any other classes but those marked as racial.