underage wizards doing magic, family protection, post-schooling

[adatole]

No: HPFGUIDX 38047

Just had to chime in on these threads.

First, I think we need to keep in mind that MOM is not exactly 
stating that underage wizards should not perform magic. More to the 
point, they are saying that underage wizards cannot perform magic 
that would give them away to Muggles. 

Think about it - Lily obviously came home and performed magic, or 
else Petunia could never have commented on turning teacups into 
hedgehogs (or whatever the quote was in SS/PS). Fred and George are 
constantly performing magic in their room, etc. I would strongly 
suspect that Hermione also performs magic at home (probably to 
practice the coming years' lessons and be prepared!). The difference 
between all these folks and Harry is that the adults around them 
support this activity, and would never tell anyone outside the 
confines of the home.
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In regard to Harry's protection in the Dursley's house - I would 
personally avoid over-analysis. Just like the whole "Mother's Love" 
protection thing, it is no more and no less complicated than that. 
Harry was protected by Lily's sacrifice of love. He is protected by 
the bond of family he shares with the Dursleys (whether they like him 
or not). Voldemort could walk up the front steps and knock on the 
door, but there is some reason he could not harm Harry in that 
environment (or else he would have tried by now - even by sending 
Peter). 
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For post schooling of wizards, I would presume that this follows the 
other conventions we have seen. Wizards have "locked" themselves into 
the vaguely medieval world. They don't have an equivalent of a 
television, radio, or even transport beyond something like a cart. 
(discounting the Ford Anglia, of course). Therefore I would expect 
that post-school age wizards usually follow an apprenticeship of 
sorts, and enter their professional lives after on-the-job 
experience.