Hi Lou
Eligibility for PIP is firstly related to a claimant's health and medical conditions. A claimant would continue to get paid even if they retired from work early.
Age only becomes a factor when claiming PIP when a claimant reaches State Pension Age. If a person has reached SPA and never claimed PIP - they wouldn't be able to apply and would have to claim Attendance Allowance. If a person has reached State Pension Age and only has a standard mobility award, they can never be awarded enhanced mobility.
So your PIP will continue to be paid.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
