Premarital relationship

I am studying architecture 3rd year. I am 22 years old. I like a boy who is 3 years younger than me, he is still studying mechanical engineering and is in 2nd year. We both will be completing after 2 years. I spoke about that boy to my mom and she didnt even consider it as his family belongs to a middle class or does not stand with our family status. She strictly rejected it as he is also 3 years younger than me. He is a well mannered person and his character is good as well. I feel that this is more than enough to consider in spouse rather than wealth and family background. I feel that there is no such restriction in Islam when it comes to the age of marrying and moreover our Prophet (sallallahu alaihi wasallam) was 25 years when he got married to Hazrat Khadijah. I said that I will complete my studies and by that time he will be completing his engineering as well and we both looking forward to getting married. My parents are not listening to my wish and are forcing me to marry someone of their choice. Because of all these issues in my home, I am unable to concentrate on my studies. Please help me in resolving this matter.