... this time to training and thus achieve a success.
Last, but not least, I do not see a reason why' should anyone' (zla kolejnosc slow, tutaj 'anyone should') do things which they do not like and do not want to do 'it' (niepotr slowo, ale i tak zle, bo masz things'-l. mnoga, to nie mozesz uzyc 'it') in the future.
On the other hand, it is generally agreed that a professional athlete can only 'be' (nie, 'be' znaczy tutaj 'zyc' oni zyja dluzej, ale nie moga wykonywac tego juz zawodu, trzeba 'participate in the sport') until about forty years old so after that there is a need to look for (przedimek) way to earn money. Moreover, the lack of 'the' (niepotr) occupation could be a big problem after the end of their sporting career. What is more, it is said that being a professional athlete is (przedimek) very hard way and only the best and most talented people can achieve 'a' (wg mnie tutaj niepotr) great success.
To sum up, (przedimek) decision to become a professional athlete could be a great chance (tutaj mozesz dodac ...in order) to achieve a great success (daj tutaj przecinek przed slowem 'but') but those teenagers should be absolutely sure that they want to be 'a' (nie potrzeba przedimka przed l. mn) professionalists 'beacuse' (ortgo slowo jest 'because') of (przedimek) many dangers of this choice.
Jeszcze raz popracuj nad przedimkami......(a, an, the)