Your V5 gives your buyer all the information he needs
Date of 1st registration (anywhere) - 5/2/1999
Date of 1st Registration (UK) - 5/2/1999
Declared NEW at 1st registration.
You bike has never been registered anywhere else. It has only been registered in the UK. When it was 1st registered it was New.
5/2/1999 is just short of 25 years
Unfortunately it doesn’t get you over the 30 year mark
I do not know if DVLA will give you access to the V55 document used to obtain the 1st registration document. If it was a V55/4 it was a new vehicle. If it was a V55/C it was a used vehicle.
contact.dvla.gov.uk