sulflower in that case my mum is a Sahm - she's in her 70s, youngest child is 40, worked full time without our childhoods, but hey, she is a mum who stays at home, therefore she's a Sahm not a retired [profession] according to you.
Of course that devalues Sahm because it gives ammunition to those who hate sahms and claim that full time work outside the home parents do "everything a Sahm dies and actually work full time" 
Which is delusional of course.
Sahms/ sahds do childcare all day, including the hours during which employee parents are not available for childcare.
If your youngest is primary age, especially infant, there is wrap around and holiday childcare so it's a grey area, but calling yourself a Sahm or sahd when your youngest is secondary age does make a mockery of the idea that sahms work hard all day and are not ladies of leisure or lazy, or set women back 50 years choosing to live off men and spend all day indulging themselves at the gym and drinking smoothies/ coffee in leisure wear - all things I've heard said about sahms which really rankled back when I spent all day looking after under 3s.
Sahms/ sahds SAH predominantly to do childcare.