Meeow, Happy COTD to Shansi! You are one very rare and handsome cat. Wonderful that at 18 you look 7. Our KatMa looked up male tortie information in Wikipedia (we don't know how exact information is from this source). If the information is correct then this how you came about:

from http://en.wikipedia.org/wiki/Tortoiseshell_cat
Coat coloration in cats is complex, and controlled by several genes. One gene involved has two alleles: the Orange allele, O, which is the dominant form, (XO), and produces orange fur; and the "Black" allele, "o", which is the recessive form, (Xo), and produces black fur.

For a cat to be a tortoiseshell or calico, it must simultaneously express both of the alleles, O and o, which are two versions of the same gene, located atthe same locus on the X chromosome. Males normally cannot do this: they can have only one allele, as they have only one X chromosome, consequently virtually all tortoiseshell or calico cats are females. Occasionally a male is born (the rate is approximately 1 in 3,000 [3]). These may have Klinefelter's syndrome, carrying an extra X chromosome, and will almost always be sterile or they may be a chimera resulting from the fusion of two differently coloured embryos.
Our Katma & Paw-Paw have a special place of love in their hearts for tricolour cats. You are adorable and your humans are so lucky to have you for 18 years. Live long, loved, cherished and adored. That is what you and every pet deserves.

Kittykisses and purrs from me, Norman the King and my baby brother, Felix the Prince. Endless adoration from our purr~ents.