Kanji Questions: Counters for the Win

This Japanese news segment seems to be using 代 (dai) instead of 歳 (sai) as a counter for age in decades as opposed to years. But if that's the case, why are the accompanying numbers also in multiples of ten? Maybe [N]代 in that sense means [N]歳ぐらい (around that age)... in a very rough, in-that-decade sense, anyways?

While on the subject, it's also sort of interesting that the counter for wins is 勝 (shou), which is the kanji for the verb for "to win" (勝つ, katsu), while the counter for losses is 敗 (hai), which is the kanji for 敗れる (yabureru), not 負ける (makeru) as I would have expected (since I've usually seen makeru and katsu paired as antonyms). Both are antonyms, of course, but I wonder why 敗 is chosen over 負 in that case.

Edit: Edited for clarity.