In model theory, the age of a structure (or model) A is the class of all finitely generated structures that are embeddable in A (i.e. isomorphic to substructures of A). This concept is central in the construction of a Fraïssé limit. The main point of Fraïssé's construction is to show how one can approximate a structure by its finitely generated substructures. Thus for example the age of any dense linear order without endpoints (DLO), One can easily see that any class K that is an age of some structure satisfies the following two conditions: and . The same applies to integers.