Starting my first concerto soon, very excited. Mozart no.12 quite a small one and a good starter according to my teacher, I am 14 and this is as stated above my first concerto, and it led me to wonder how old were other people when they played their first concerto? And another question, because I am playing it in a competition (chethams summer school international concerto competition) is it acceptable for me to make up my own cadenza?

I guess you could make up a cadenza, but unless you're a genius I would play the one Mozart wrote... (assuming he did write one for that concerto, I'm too lazy to check )

I was around 12. It was the Haydn D major. My next concerto was your piece, the K.414 in A major. I was 13. It's small, but it's lovely. Work on clean playing with stylistic pedaling and try to wow them with your trills, such as the melodic trills in the recapitulation. I still have my copy of the piece from 45 years ago with "double triplet" written in by my teacher.

The Mozart is definitely a step up from the Haydn. Your teacher is right in that regard.

Although there probably are no rules against playing your own cadenza, I would stick with the Mozart cadenza unless, as somebody said, you are yourself some kind of prodigy. A fiery cadenza that is unstylistic would be just as likely to turn a judge off as it would be to impress her. Play the Mozart cadenza. Just play it well.

I would use a cadenza that is already written for this venue, if I were you. In Beethoven concerti one often has more than one to choose from. If Mozart didnt give you this option (I haven't played this particular piece) then I would use the one he wrote, but get hold of as many different recordings as you can of it and listen to all the different interpretations to see which one you really like the most (or some combination thereof) and craft your cadenza accordingly. Just MHO.

Your teacher made a good choice. If you are not able to play it with an orchestra, Mozart himself offered the option of playing it with a string quartet. You can buy the Bärenreiter edition with parts, or you could get parts from Kalmus if you are not so much into fancy editing.

As for the cadenza, Mozart wrote two alternate cadenzas for each movement, which I would take as an invitation to make your own choices. I think you should try all of them, so you get an idea of his style, and then if you feel like writing your own, go ahead! You could also come up with some other fermatas, besides those that he wrote.

Have fun, and remember, even if you do not win, you can still play it with other musicians.

My first concerto was the Haydn D major and my second was Mozart No.12. I performed the Haydn (with orchestra!) at 14 and the Mozart a year later. (I too still have my score, 46 years later, with "up" written at the end of almost every phrase.) The cadenzas Mozart wrote are lovely, and unless you can outdo them, I would use his.

My first concerto was the Haydn at 10, and then Beethoven 1 at 11. I played Mozart No. 23 later that year.

Mine was the Grieg Concerto at my current age (18). My second was Totentanz (as of 2 weeks ago), at my current age. Hopefully I get to perform Totentanz with an orchestra in October (fingers crossed!). If Mozart wrote a cadenza for this one, use it. If you do write one, write it in the style.