When should we gift our son a property we are buying?

We are currently looking to buy a property for cash which we will then rent out.  We would like this to be for our son who will soon be 17.  Is there any way we can do this at the time of purchase?

Since your son is under 18 he cannot legally own property. So you can purchase the property in your names as the legal owners (bare trustees or nominees), so that your names will be on the official documents, and instruct the solicitor to draw up a deed of trust at the time of purchase explaining that your son has the beneficial ownership of the property. When he becomes 18 it is a simple procedure to transfer the legal ownership to him.