Is Enlightment ultimatelly up to you (Karma and Freewill)?
Enlightenment comes as a natural result of the meditation practise. When you practise meditation with proper effort you'll realize very quickly that this is path of freedom from suffering. So with experience a person realizes the benefits of meditation and that realization can lead the person to get involved with meditation more deeply. 

It is "not" possible for a person to not become enlightened If s/he is able to get rid of his physical and mental addictions, learns to practise mindfulness correctly and practises mindfulness and meditation for long periods of time. But modern life's requirements, the person's attachment to wrong ideas/beliefs and the possible mental or physical problems limits a person's conditions to do what is necessary in the path of freedom from suffering. So the chances to have success in the path is not just about freewill or karma. It's about both of them.

You don't need to be a Buddhist or subscribe to any religion or tradition to have benefits from spirituality. Also Buddhism really leads people to become Non-Buddhists If one follows Buddhism correctly. Just like Thich Nhat Hanh said "Buddha is made of non-Buddha elements". 

If you want to start to walk in the path, this map can be helpful to you: https://www.youtube.com/watch?v=ErN4a5qvxok