They are indeed full size and given a basic level of programing (speech, motor functions, in some cases a faction loyalty inclinationm etc).

However you do have 'younger' inexperienced Transformers and that is how you measure their age and maturity level.

List of popularly known 'young' Transformers:

- Hot Rod
- Cheetor
- Hot Shot
- Bumblebee (although this could be debated)

So a Transformer's age is evident in their maturity level and experience rather than visual appereance in most cases.