Is (a young-faced) 26 too old to become a model?

Of course not! You just gotta prove that to the agencies =] There is a lot of other (younger) competition out there so you gotta be tough, but i'm pretty sure that if you are determined enough then you could do really well. Being older could be your selling point - you are more 'mature' than the others and have much more 'experience' of the world around you =P Just trawl the interweb for modelling agencies and see what you can find!