When the father dies the inheritance goes to the son even if that person has a older daughter. Is this true in terms of our religion, or is it a cultural thing?

Firs of all it is not true that inheritance goes only male children or older male child, indeed, there are many verses and hadith which allocate each person his/her share from the inheritance. Unfortunately, today there are un-Islamic cultures in many countries and people assume that those practices are related to Islamic teachings. In short, man and woman have both shares in inheritance