A good place to start for image classification with KNIME is this workflow on the hub. It uses Keras to classify images from the MNIST digits dataset. To use it, you’ll need to download the Keras and Image Processing extensions, but you should be prompted to do that when you download the workflow if they’re not already installed.
For your use case, you might try a similar approach. Of course you will need to have pre-labeled input data of your own, with ages and gender already available, to build the model.