1) At your age, I did not study so hard as you did.
2) Japan was more exciting place than it was today.
then you cannot change them and keep the same meaning as in your examples. These are are not examples of reported speech. This again illustrates that reported speech is not a shift to an actual past tense verb. In the case of reported speech, using a past tense, eg "I was going to ..." doesn't give us the meaning that "I was going to ..." nornmally has when it is used in contexts where there is no reported speech.