A Eureka lemon differs from a Lisbon in that a Eureka's branches have a more spreading habit, and are pretty much thornless. Lisbon lemons are quite full of thorns. On the other hand thorns are also a sign of citrus juvenality. I not sure if this pertains to a seedling lemon, as I have never grown a lemon from seed. Your tree should have begun blooming by now. Are you pruning this tree? Any pruning of a citrus tree, lemon included, will delay, or even prevent the tree from reaching maturity, therefor it will not flower or fruit. - Millet (321 BO-)