I don't know how many prayers I have missed my entire life of 24 years, but at least I can guess the amount is (at least 50 obligatory prayers and 50 Wajib plus some more prayers when I was in traveling).
I heard that when making up those prayers one should recall the time or date of each prayer, otherwise they are not valid.
Some prayers I have made up having the intention that these are the prayers that I have missed when I was 15 years old? Are they correct? If not what should I do?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The scholars differed in opinion in regard to the ruling on a person who abandons the prayer. Some of them are of the view that such a person goes out of the fold of Islam and if he starts the prayer again, he does not have to make up the prayers that he had missed because all his deeds became void because of his disbelief [going out of the fold of Islam due to abandoning the prayer]. Hence, he is obliged to repent again and regret his sin so that Allaah accepts his repentance.

The majority of the scholars are of the view that it is an obligation to make up all the prayers that one had missed and that it is not at all permissible to be neglegent in making up the prayers, and that a person must repent to Allaah due to neglecting the prayers and delaying it from its prescribed fixed time, and he must regret this.

Therefore, according to the view of the majority of the scholars you are obliged to make up all the prayers that you had missed, and you should make them up in the same manner that you had missed them. For instance, if you had missed 50 prayers during travel, then you have to make them up as traveler's prayers, i.e. the four Rak'ah prayers you should make them up as two Rak'ah prayers only [such as Thuhr, 'Asr and 'Isha] according to the most preponderant opinion. However, the prayers that you had missed as a resident [not travelling], you must make them up in full without shortening them.

Now, if you don't know the number of prayers that you had missed, then you should perform a number of prayers by which you think you have made up all the missed prayers because you cannot be acquitted from sin except by being certain about how many prayers you had missed. Also, you are obliged to take the initiative to make up the missed prayers according to your ability at any time during the day or the night.

Besides, it is permissible to make up the missed prayers at any time while determining the intention for the prayer you are going to pray, like Thuhr or 'Asr, for example, while, of course, respecting the order of the prayers, Thuhr, 'Asr, Maghrib, 'Isha, etc. However, it is not compulsory to indicate the day or date. Therefore, the prayers that you had already made up are correct (valid), Allaah willing, if the above conditions were met.

Allaah Knows best.