Getting married with the blessings of one's parents

I am 18 years old and have received a proposal from a guy who is 32 years old. I am quite keen and I have performed istikhara and so has a moulana and both were positive. A mufti also advised me that Ayesha (Radiyallahu Anha) was much younger than the Prophet Muhammad (Sallallahu Alayhi Wasallam) and islamically it is acceptable however my parents refuse to accept. My life at home has become very miserable and I am verbally abused and sometimes even hit for my decision. I can't seem to take it anymore and I think I should take things into my own hands and get married. Please advise.