First choice, absolutely.

Best way is the honest way.

In this case, being honest isn't just for the sake of personal honor or ethical philosophy, it's better for the guy to understand clearly exactly what the situation is. There's no false hope nor bitterness over your own equivocation. He can move on and direct his efforts else where.

That's my thoughts, at least.

Accrediting him for pursuing older ladies is totally a plus though!! I might appreciate you encouraging that mindset 20 years from now.