Film Idea problems

Me and the other members in our practical group are having doubts about whether our film idea is going to work successfully. Our main issue is casting, as our storyline is based around a thirty something...year old guy. So this means a male of that age is required, and none of us know anyone of that age to help act in the teaser trailer. Another problem is successfully involving key factors of a romantic comedy genre, such as witty/sarcastic/stupid jokes and moments etc. We do not want it to look ammature, and we are having thoughts that it may look that way due to our lack of money, actors that are suitable, and the area that we live in. I personally feel that this genre (romantic comedy) is going to be alot harder to pull off than a 'Thriller' would be. We'll have to make a rapid decision soon, as we are already starting on our other smaller tasks that go alongside the teaser trailer.