This link will take you to a checker tool on the .GOV.UK website where, if you are in receipt of D.L.A you can enter your date of birth and the tool will tell you the date when you will be invited to apply for P.I.P
The example shown below is for someone borne on 10th May 1982.
"You shouldn’t be affected by Personal Independence Payment (PIP) until 2015 or later, but there are some exceptions.
You’ll be asked to make a claim for PIP if after October 2013:
• There’s a change in how your condition affects you.
• Your Disability Living Allowance award is due to end and you haven’t received a renewal letter.
Unless either of these happen – you don’t need to do anything. You’ll get a letter in 2015 or later explaining:
• What will happen to your DLA.
• How you can claim Personal Independence Payment."