I read your requirement and I have implemented exactly what you require - API to detect age / gender- you could check my portfolio.
For demographics prediction, we would require retraining the model, and with frontal face images.
For text/sentiment analysis we could use Alchemy API.
I am Pranav Patil, representing Iristechsys Software Services LLP, an ISO 9001:2015 company based out of Pune, India.
Our company has a valid DUNS number and is duly registered with Registrar Of Companies, India - just to point out that we are *not* a fly by night operator.
My Linked-In profile will provide you overview of my experience.
The best part is that we wont charge you if we couldn't achieve the results that we have promised.
Please provide us an opportunity to demonstrate and I promise we will not disappoint you for sure!
Regards
Pranav