Nick ...
... what Rob just said. Don't take it personally.
There are just some adults in this world who do not consider under-agers worth their time. $30 in bags is one thing. A $2,000 vacuum is quite another. And a customer satisfied with her $2,000 machine who will bring OTHER adults with their checkbooks is definitely another.
Just continue to be pleasant. You'll win him over eventually. I was you back in the early '80s: 13 years old, and always wanting to go down to "Central Radio and TV" in my hometown; that was THE store for high-end electronics at the time. The owner was nice enough, but really only let me back into the "back" display room (with the REAL good stuff) when I was with my dad. But over the course of a year or so, seeing how I absolutely revered the equipment, he started letting me back there on my own. His wife really liked me too.
It got to a point where they trusted me enough to actually extend me credit (to a degree); the owner made it quite plain he didn't do this for any other customer, but there was a receiver I wanted in the absolute worst way. It was one of the last great receivers made in the USA by Zenith, complete with flywheel tuning and both hi and lo filters. I just adored it, but it's retail price at the time was an ungodly $679 (adjusted for inflation, that's $1,540 in today's dollars! For a 13 year old, no less!).
Well, as it happened, it was 1983, and the new trend in receivers was now DIGITAL. No one wanted analog tuners, even with the fabulous flywheel tuning. Nor did they want analog VU meters; they wanted the newer gradient LEDs (which have been all but abandoned these days on higher-end equipment, but it was the fad back then). In other words, that fabulous old Zenith -- along with the other '70s beasts of the day from Pioneer and Kenwood -- were now white elephants. They marked the price down by 70%, but it was still more than $200 -- still completely out of my reach.
With those markdowns, the owner was finally moving those big beasts. But I didn't want to lose my beloved Zenith. The owner recognized this and cut me a deal: he'd put it layaway for me, as long as I made regular payments every single week. OMG! It took me an entire summer of grass-cutting money, but that day back in September of 1983 -- that beauty was in my bedroom. Out of all the possessions in the world, that is the one thing I absolutely will never part with. E V E R.
My point is, I won him over. My dad told me later on that the owner pulled him aside and said he actually LOVED selling me that unit, because out of all of his well-heeled customers, he knew *I* would appreciate that unit the very most.
Over the years, his trust in me grew to the point where he would let me take merchandise out of the store to try it out before buying it! And this while I was still in high school.
Just be patient. You'll win him over one day.