You can definitely make bookings for someone else. Following are the methods you can use
Book an e-ticket and forward the confirmation email to the traveller.
They can then download the e-ticket from there on their phone or print it.
Download the mobile app and book tickets from there. Make sure you enter the traveller’s information and not yours. Send the confirmation email to the traveller and they can carry it on their own from there.
You can also send them the PDF file of the ticket which they can simply print
Book the tickets for whoever you want to and enter the address of the traveller rather than your own for collection by post.
Lastly, the traveller can collect their ticket from the self-service ticket machine available on hundreds of stations using their collection reference number.