| I'd say it's case by case.
A 7 year old is not going to want to practise guitar every day regardless of whether they're physically able to or not. At 7 years old, your idea of a lot of homework is the rest of that spelling page you didn't finish in class. Practice boring songs on a silly instrument for a whole half hour every day? Not a chance. Now there are exceptions where the kid actually wants to learn.
Though a lot of it doesn't have to do with age at all. Most people have this expectation that by simply showing up to their lesson every week having played what you told them to play once the night before, they'll become amazing. This happens with people regardless of age. If people aren't willing to put effort in, they're basically wasting their time with you.
I would say you should take any age, but if they're too young, then tell the parents that.
Oh and as for physical limitations, you can usually find a way around them. For the first 3 years I took piano I couldn't reach an octave. Somehow my teacher found a way around it and played at a grade 5 RCM level...
__________________ If I speak in the tongues of men and of angels, but have not love, I am only a resounding gong or a clanging cymbal. If I have the gift of prophecy and can fathom all mysteries and all knowledge, and if I have a faith that can move mountains, but have not love, I am nothing. If I give all I possess to the poor and surrender my body to the flames, but have not love, I gain nothing. Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. - Stephen Hawking |