I agree with those who have suggested that formal education is more important, and that bravojs would do well to focus his time and energies on studying for his A levels.
There is truth to the argument that one needs periodic breaks from studying; but I would respectfully suggest that such breaks should be many and short (e.g., two one-hour breaks each day) rather than few and long (i.e., one day flying every week). Additionally, break time is probably best spent doing something relatively mindless (going for a walk, etc.), rather that flight training (which requires a reasonable amount of effort, including preparatory reading, if one is to get much out of it).
IMHO, I don't think that it is quite fair to encourage him to go flying based upon anyone else's history of obtaining their PPLs during university. For one thing, university programmes (especially Ph.D. programmes) tend to be considerably less structured than secondary education. For another, bravojs says that his "latest test results(academic) shows that i am really far behind in my work ...". It may be that he is not particularly gifted academically, or is challenged by language difficulties or other individual circumstances ... he should not feel pressured to live up to other people's successes.
In any case, as bravojs is looking ahead to a lenthy and mandatory break in his flight training (during national service), it might be best to simply put the flying on hold. One way or the other, there will be a significant re-learning period when he resumes flying; there's no point in potentially shortchanging his academic work, simply to enter hours in a logbook.
In my respectful opinion, the 'bottom line' is that one can complete a PPL at pretty much any age, and there is no shame in taking a while to do so. On the other hand, there's no pleasure in re-writing A levels or similar examinations in one's late 20's or whatever. Best to make a solid and focused effort now, lay the groundwork for a successful and reasonably lucrative career, and there will be plenty of time left for flying later.