First of all, it is Allah that lets you have the attention to pray, and that he wishes you to pray and to reward you.
Secondly, there are people who are being tortured in the graves, who have never prayed to Allah once, and even when you pray today, there are those who wish to enjoy the life of this world.
Thirdly, your setting yourself a too higher goal to be done so quickly, we don't of course normally calculate how long it takes for us to pray (as we don't accept rushing), but its good on this occasion to have a fair idea, so lets say it takes 5 minutes to pray 2 fard in the morning. (As lets remember that your making up for the fard prayers not the obligatory ones). So if you prayed for an hour for the 2 fard you would have done it 12 times.
The next step is to start smaller, complete a prayer for month by month. So if you you prayed 12 fard for the morning prayer, then that would be about 2 and a half hours. So by praying for 2.5 hours of prayer of 2 fard you would have completed a month's prayer of the morning.
The step after that its to complete the rest of the prayers. You can complete them in continual order of the morning prayer and then the noon prayer etc. As you are unable to of course complete them all in set times ie in sunset you can make up the prayers when you set the time to do that. Regardless of what people may say, you are absolutely relying on Allah's mercy to accept them, and no one can say that it can't be accepted.
So if you set another 5 hours a side to make up the for morning prayer (were your reading the fard one only), you can possibly make up a month's prayer whenever you set time for it -it can be done in a week or 2. So if you did that in 1 week, you could make up one year of prayers in 12 weeks (if you allocated the rest of the prayers to make up for)- 3 months, and then of course if you kept to it per week for example, that is 1 year prayer per 3 months so that's 4 years of prayer in a year. You can keep a timetable -get a pen paper ready, when you wish to make up for prayers and in which order, and keep track when you have started on what you have done (this is solely to give you a peace of mind).
The above example is if it took you 5 hours of the noon prayer (to make it up for a month), 5 hours for the isha prayer, 2.5 hours for the fajr prayer, 5 hours for asr prayer, 3 hours for the maghrib prayer= 20.5 hours per week so that is just about 3 hours a day of setting a side for prayer or even less to 1.5 hours a day if for 2 weeks. So you would have made up a month's prayer in 1 week or 2, so go month by month.
I STRONGLY suggest that you create a timetable to make it easier, that you don't push yourself over, the above example just makes it easier to understand that it can be done -its just about organizing yourself.
The rest you leave to Allah to allocate your prayers to the missed ones, so you do a rough calculation, but I would start backwards, so for example if your 27, and you started missing your prayers from 13-25 years of age, you start your intention by making up your 25 year, then your 24th year, then your 23rd year then Allah if you do that can allocate the rest of your prayers to when you were 13 years of age (to usually a childhood age of innocence). So all your doing is a rough calculation and then letting Allah from your intentions place it on your records that you have prayed).
Don't forget that is what Allah will be asking for on the Day of Judgement, of how many times you have prayed, a day when there are wrongdoers that have never prayed in their life. So as above, only has a guide and that don't give up hope and it can be done. :sunny: