I am doubtful, if I can show my bank statements and funds to sponsor my younger Brother's visa, who is definitely above 18, but is a student. He is planning to visit my elder sister in Germany.
When your brother applies for his visa, he must convince the immigration officials that he is a genuine tourist and will not overstay.
- He must explain his financial circumstances and demonstrate that he has good reasons to return home.
- He must explain where the money for the trip comes from, and that it is reasonable to spend this money on a luxury like tourism. It must be clear that the travel expenses are not an investment that will be repaid by working illegally.
So regarding your gift of money for the trip, the question is if it is reasonable for you to give the money. That depends on your income, expenses, and savings, and on your relationship to the recipient.
Looking at your Stackexchange profile, it would seem that you can afford the cost of a trip to Europe for your brother, and being an older sister explains why you would give him the money. So there should be no trouble in this regard. But your brother still has to submit his bank statements. Yours will explain the second bullet point above, but not the first.