The bitcoin still has to get bigger to reach what paypal has done, also I think you cannot compare them.
I am quite sure that with all the potential growth that Bitcoin can realize the coming years, that Bitcoin will come very close to the USD transaction volumes. Right now PayPal has a transaction volume of $24 billion per month, while Bitcoin's transaction volume is sitting at around $4 billion per month. Where Bitcoin has still a lot potential growth to gain throughout the years, is PayPal currently peaking at the moment. I don't think PayPal can continue its growth. It will slowly show a lower and lower growth where they eventually will lose market share.