Dan,
like u said, if usia dah senja, den anak pun dah cukup quota, healthwise pun tak mengizinkan, yes, why not ligate kan?
but yg muda2 tu... bukan tak boleh.... but fikirla panjang2...
personally, Insya Allah, wen i'm 35-40, and confirm tak ADVISABLE to branak lagi, i mite just ligate... bukan aper.. takut dah nak retire, tapi masih kena ulang alik gi antenatal cek up! hehhehe