Q. A bachur who makes some money (such as when he leins or participates in a learning program) but is generally dependent on his parents for his sustenance, is he obligated to give maaser from the money that he makes?
A. Poskim mention that a bar mitzva bochur should begin giving maaser as he also complies with other mitzvos (Beorach Tzedaka 3: 7, quoting R”P Sheinberg and R”N Karelitz Shlit’a).
As far as he being considered an oni or poor and exempt from maaser, as mentioned in the prior question, Shulchan Aruch (248: 1) rules that everyone is obliged to give tzedaka, even one who himself depends on charity to survive. See also Orchos Rabbenu (3: p. 138) quotes Chaye Adam (p. 295: 5) and Chazon Ish, assert that even the impoverished that survive by receiving tzedaka are obliged in the mitzva of tzedaka.
However. Mishne Halochos (2: 152) relieves an oni from giving maaser. Beorach Tzedaka (ibid.) maintains that most Poskim exempt him from giving maaser.
Horav Shlomo Miller’s Shlit’a opinion is similar.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a