Qaza fast is obligatory on you as soon as you can. If you become permanently ill and never able to fast, then you need to feed for every day a poor believer which is called Fidya. That is for the days missed while you are ill. For the days which you missed during your youth with out illness, you need to feed sixty poor believers for every day of missed fast.
This is a very important question for those who really care to improve themselves and achieve better degrees of success in this life and hereafter. These are few practical steps which can make the believer more close to Imam-e-Zamana (AS). More piousness leads to more nearness to Imam-e-Zaman. To add to our Taqwa (Piousness), these are few points:
1. Asking yourself before any act or word whether Allah (SWT) likes it or not? That is the best degree of remembering Allah (SWT) along with continuous remembering him in our heart and tongue.
2. Reciting Quran and Du'a with understanding and pondering and gifting its reward to Imam Al-Mahdi (AS).
3. Performing Nawaafil prayers especially Night Prayer ( SALAT ALLAYL or NAMAZ E SHAB) every night.
4. Talking to Imam e Zaman (AS) every day and night as he listens to us and responds to the pious believers.
5. Gifting the reward of all our good deeds to Imam Al-Mahdi and all Ahlul Bayt (AS) which will not only multiply our reward, but also make us more near to them.
6. Having best Akhlaq (Manners) with parents, relatives especially your family members and with all people.
7. Being with Wudhu all the times as much as you can.
8. Trying to strengthen our will power by avoiding evil desires and performing good acts even if it can look like difficult like fasting, charity,etc. We need to control our desires and never allow our desires to control us.
9. Helping needy people in any possible way for the sake of Allah (SWT).
10. Trying to make believers happy by respecting them, caring for them, smiling in their faces and in any other act of generosity and kindness to them or their families.
11. Performing obligatory Prayers on time with out any delay. Imam Al-Mahdi (AS) performs every Prayer on time, so, your praying on time will make your Prayers elevated to Allah (SWT) with the Prayer of Imam Al-Mahdi (AS).
12. Keep your most important supplication and wish, the reappearance of Imam Al-Mahdi (AS) and sincerely pray for him more than praying for yourself and your family.
No doubt at all that Imam Hasan (AS) and Imam Husain (AS) are the two masters of all the youth in Paradise. This fact has been mentioned in many Hadeeths in Sunni and Shia books. The Hadeeth states also : Their father is better than them وأبوهما خير منهما. Al-Mustadrak ala al-Saheehain by al-Haakim al-Nisabori , V.3, P.182.
All believers in the Paradise will be young even if they dies in old age. There will be no old age in Paradise. The masters of all in the Paradise will be the Prophet Muhammad (SAWA) being the Best of all creatures, then Imam Ali (As) as it is mentioned in the Hadeeth, then Imam Hasan (AS) and Imam Husain (AS).
This may be too complicated for youth, who sometimes need things to be black and white or absolute.
As Muslims, we like to see Islamic law as fixed and perfect and absolute, an exact copy of the divine will.
However, in reality, the derivation of Islamic law is a process. Some rulings are stronger than others.
For instance, it is obvious that drinking wine is prohibited in the Qur'an. There is 100% certainty on that viewpoint.
However, it is not obvious that a marja' must be a man. This is more of a viewpoint that has been deduced based on assumptions about the ideal social role and nature of women, as well as some sideways derivations from texts. (Probably, the era and cultural environment of these discussions also had some effect.) That is, we don't have an ayah or hadith that specifically says "a woman cannot be a marja'" in the same way that the Qur'an says "do not drink wine".
However, instead of understanding the process of how rulings are made, some Muslims start at the result and go backwards. That is, they take the ruling that "a woman cannot be a marja'" and then, from it, deduce all sorts of things about the role of a man or woman in society. This is a sort of layperson's error that comes from a pious but incomplete understanding of the Islamic scholarly tradition.
So... the short answer is... yes, it is a common viewpoint that a woman may not be a marja'; however, one can also make a case that it doesn't matter if a marja' is a man or a woman. Perhaps, the dominant viewpoint on this may change in the next couple centuries.
This is all theoretical; it is unlikely, in the present day, that a woman will actually become a marja'.
As for how you wish to discuss that with the youth... that is a more challenging question. My personal approach to dealing with young people is to try to be as honest as possible; at the same time, if they are growing up as a minority, sometimes they really need the sense of solidity of everything in their faith being 100% certain and agreed upon, at least up until a certain age. Perhaps someone else may be able to advise on this.