I'll second CL's comments on working on self control rather than relying on numbing agents. Personally I find that if we get into a steady sexual routine I can control myself much better. If we go for a while with no sex, I find I don't last long at all, and have to work very hard not to cum instantaneously.
And I'll also agree that my lasting ability has not changed as I've aged. For me it has more to do with frequency of sex.
