Your entitlement to drive this vehicle depends on both its weight (the maximum authorised mass, or MAM) and also the entitlements on your licence. As you likely passed your driving test before January 1st 1997 you would have had a C1 entitlement which would allow you to drive vehicles up to 7.5 tonnes. However, unless you specifically applied to retain these categories when you renewed your driving licence when you turned 70, these entitlements will have been lost.

You can reapply for them via the DVLA but you will also need a medical report from your doctor, and you can obtain the forms required to do so on the DVLA website here: www.gov.uk/dvlaforms