Dear, sir.
Nice to meet you and thank you for taking the time to read my proposal.
I am a mobile developer who has more than 6 years of experience of iOS and Android app development.
As a senior mobile developer, I have developed many apps before and uploaded it on app store, so have the rich experience in mobile app development as well web back end development.
I like to development, love coding, my working and also very interested in working for your project.
I'd be more than happy to offer my service for you and I'm excited to hear from you.
Kind wishes.