Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
The obligation to give Zakat does not expire in time, so if anyone, who failed to pay it, has to compensate for it, according to Sheikh Khalil, may Allah rest his soul in peace. The same view was expressed in the Tahdhib Al Mudawwana, which says that the able Muslim must pay the accrued Zakat for all the years missed.
Accordingly, you are advised to give your Zakat in time as long as you are able to do so. What is more, you do not need to pay any extra money because of your delay. All you can do, however, is either give it in kind (roughly 2.5 kg of rice or dates, etc) or in cash (determined in AED 20) per person.
As for your second question, since you do not own the Nisab over the year, you are not supposed to pay any Zakat. Still you can give charity, as our religion has urged us to engage in such an act of goodness. It was reported from Abu Huraira that the Prophet Muhammad pbuh said, "A Dirham was better than a hundred thousand Dirhams." They said, "O Messenger of Allah, how?" He said: "A man had two Dirhams and gave one in charity, and another man went to part of his wealth and took out a hundred thousand Dirhams and gave them in charity." And Allah knows best.