Further to my previous comment, PIP is only eligible for new claimants of working age (16-64). However, the Government is in the process of reassessing all previous Disability Living Allowance claimants for PIP. DLA claimants will be reassessed for PIP if they were aged 16 to 64 on or after 8 April 2013.
So it’s strictly true that some historic DLA claimants could be older than this and still come up for PIP assessment, but new PIP claimants can only apply if they’re of working age.
I hope this information is useful.