Key limes are frequently grown from seed since it is “true-type”. The seeds are poly embryonic, meaning more than one embryo. This results in multiple trees being grown from one seed. Sweet oranges will come true from seed, as well as grapefruit, tangerine and tangelo. Key limes may also be grafted with hard wood cuttings, with air layers or as budded trees with rootstocks resistant to foot rot.
There are some distinct advantages to both of these methods. Simply sowing the seeds eliminates the need for a grafting setup. Seedlings are more likely to be virus free, which seems to be a problem when grafting large numbers with bud wood.
There are reports that non-grafted citrus trees live up to twice as long, as grafted trees. Apparently this is determined by the number and types of disease organisms that may be present in the bud wood. If you are able to obtain certified disease-free bud wood then there should be no difference in the longevity of the trees. The seedling tree might not bear fruit for up to 6 or 7 years. In contrast a grafted tree will produce fruit within 3 to 4 years.