Can We Pray after Masturbation without Ghusl?
Question

I used to masturbate since I reached puberty and I did not know that it is prohibited, and I used to pray without doing Ghusl. Now I have repented, praise be to Allah. 
My question is: should I make up the prayers that I missed with every obligatory prayer, or should I offer them all at one time? Should I offer them in order i.e., should I start with Fajr first and then Zuhr and so on?
Praise be to Allah.Deliberately praying without having purified oneself is a grave sin , and the one who does that comes under the same ruling as one who does not pray, because he has failed to do something without which his prayer is not valid . 
Ibn Al-Qayyim (may Allah have mercy on him) said: 
“The ruling on not doing Wudu or Ghusl in the case of major impurity, and not facing the Qiblah when praying, and not covering the `Awrah, is the same as the ruling on the one who does not pray. Similarly the ruling on not standing, bowing or prostrating when one is able to do so is like the ruling on not praying.” (As-Salah wa Hukm Tarikiha, p. 42)
It seems from your question that you did not do Ghusl in the case of major impurity because you were unaware that it is obligatory. The scholars differed concerning one who does that – does he have to repeat the prayer or not? 
If it never occurred to you that it is obligatory to do Ghusl after masturbating, then we hope that you do not have to make up the previous prayers , but you have to repent and be righteous, and do a lot of good deeds. Allah say (interpretation of the meaning): 
“And verily, I am indeed forgiving to him who repents, believes (in My Oneness, and associates none in worship with Me) and does righteous good deeds, and then remains constant in doing them (till his death).” [Ta-Ha 20:82]
And Allah knows best.