I'm 49, unfortunately. And I've been using fountain pens since I was 11, when someone bought me a cheap steel-inlaid-nib Sheaffer for Christmas. (I say 'cheap', but it was expensive compared to a biro, and I was overwhelmed by its preciousness.)
A bully called Brian Crocombe tossed it in the air in the school playground, and it died. (I'm afraid karma has yet to catch up with Brian.)
I have been using FPs ever since. But it is only in the last two years or so that I've realised how bloody fabulous mechanical pencils are.
I now use - far more than any pen - a Pentel P205. It's sort-of the standard MP, as many of you know. What makes it truly a great writing instrument, though, is the Pentel Ain Stein leads I stick in it.
I use 4B, and the darkness and smoothness are spectacular. This combination writes wonderfully on nearly every paper, though paper is still a consideration for the best performance.
I am usually very happy to carry this MP with this lead with my notebook, because it is almost - almost - as pleasant as a Safari or Pelikan.
And if fountain pens were disinvented, or if the government of my country suddenly decided (in a fit, perhaps, of puritanical zeal) that fountain pens were a vanity too far, I think I could just about cope.