It could just be that the pop up was delayed and he actually got the skill up much earlier, I've had delayed pop-ups lots of times for skill challenges, I'll complete a challenge I've been working on, and I know I've completed it because I checked I only had to, for example, seeing as this about charisma, meet one new person to get celebrity, I'll have my Sim introduce themselves to somebody, get no challenge completed pop-up, check the log and see the challenge bolded in as completed, shrug and get on with the next thing, and then hours later there'll be a pop-up saying '<insert name here> has met loads of people and now everyone likes them' (or words to that effect) and I'll be like 'Really? you only just noticed? silly computer!'
Personally I love Charisma, I try to remember to send my newly teen-aged Simlings to a mirror to learn that first point as soon as possible, even at low levels it helps so much with making friends or seducing the younger siblings baby-sitter or whatever, and then unless the Sim in question has a need for Charisma for their job or something, I just ignore it and let it raise naturally, as it's capped by number of friends loner or housebound Sims don't end up with unrealistically high levels either, which is nice. I just wish Sims in Sims 3 could learn it before they become teenagers... can we have the annoying pink bunny toy back please?