i think it is always difficult to offer advice about buyers when we are more interested in the construction. both andy and tim are right.
however you have made a really good start, but i wonder whether painted finish is the right way to attract customers. painted finishes are too similar to those produced in a factory situation, thus i would suggest that unless a customer particularly request paint, you should go for a stained finish, it immediately makes the product look more hand made, and thus more likely to be more expensive.
congratulations on producing such a nice piece, and take no prisoners about your age, you obviously have a skill, maybe now is the time to think about a college course, or become an apprentice to enhance your ability.
i think another thing to do is make a couple of pieces to show people, so that they can see your skill, and more easily determine its value.
it is a shame that in the same month that the Jimmy Carter Foundation in America sells a cabinet made by the ex-President, for over $1million, woodworkers in the UK would rather make built ins because they are not then in competition with the retailers. Saw a nice outside looking cabinet in John Lewis recently for about £600.00, but the inner details were real rubbish, and that is where we should score,if only its pointed out.
keep on making and showing us (up?) you will get the plaudits you deserve. must say wished i'd had such a workshop at your age.
all the best
paul