Actually you can say the same sentence these ways in Spanish: "Este año no he ido a nadar aún" "Este año aún no he ido a nadar" "Aun no he ido a nadar este año" "Aún no he ido este año a nadar" "No he ido aún a nadar este año" "No he ido este año a nadar aún" "No he ido a nadar este año aún" Mybe I personaly prefer the three first sentences. But all of them are correct. Yes! You've chosen the perfect verb tense!, because the year hasn't ended yet :) Good job!

You have to put the "aun" before the "no" but you are using the perfect tense (pretérito perfecto)! :)

aún = yet, since you didn't include it in your English phrase then it would be "Este año no he ido a nadar"

It's correct. You can say both. -Este año aún no he ido a nadar. -Este año no he ido a nadar aún. Also you can use "todavía" instead of "aún".