個

1. counter, also written as ヶ counter for (small) things or pieces
2. counter for military units
3. noun (an) individual; one person
4. counter, colloquial counter for years (of age difference); counter for school-years

か also 箇

1. counter, usually in kana, precedes the thing being counted; e.g. ３か月, ５か所; also written as ヶ or ケ counter used with Sino-Japanese words

つ

1. counter, usually in kana, suffixed to Japanese numerals 1-9 (ひと, ふた, etc.) general-purpose counter
2. usually in kana ... years old