Can a co-owner of a vehicle be considered a "principal operator" of the vehicle?

I cannot agree. The description of the vehicle use defines the rate class for insurance purposes. The description here makes it clear that the rate class comprises owners or lessees who are at least sixty-five years of age and who are the principal operators of the insured vehicles. On the other hand, condition 7 can mean one of two things. Either it means that a co-owner can be under age sixty-five but the other owner must be both age sixty-five and the principal operator, or it can mean that the co-owner, who is the principal operator, can be under age sixty-five so long as the other owner, who is not the principal operator, is age sixty-five. The first meaning reconciles easily with the description of the coverage, but the second meaning conflicts. Thus, the latter interpretation must be rejected in accordance with the principle that statutory language must be construed so as to give the words a sensible meaning: Curtis v. Stovin (1889), 22 Q.B.D. 513 per Bowen L.J. at 517.