Its a common sense to purchase tickets when you use public transport services. I don't think anyone shall have the right to get away from purchasing a ticket just because he/she is old or doesn't understand the language well. How does a person know the way to a destination without being able to understand how the transport system works? He/she needs to understand a map to the least. If some people suffer from disability or come from a low socio-economic background, the welfare system is there to support them with concession cards, which are very legal.
From what I know, many people, whether old or young, have been taking advantage of the fact that you may get away from being fined if you pretend you did not understand the language.