DD is almost 13 months. She slept well from about 4 weeks - 8 months. With that I mean waking 1-2 times a night for a feed and going straight back to sleep on the boob (we co-slept full-time for the first 6 months and co-slept after her first night feed from 6-12 months). However, from 8 months on, after the first 2 teeth had popped out, things went progressively worse. Around the time of her birthday, I was at the end of my tether as she had taken to waking every 45-90 minutes. And sometimes around 4 am, she would have real troubles going back to sleep. At tother times, shed fall asleep on the breast quite easily. But I wasn't prepared to feed her up to 10 times a night anymore.
So we gently made some changes. Like cutting down to only one day sleep, and trying to settle without the breast (DH had to help there, mainly on the weekends, though) at most times (I had made a rule that she doesn't get fed before 12 and then not again until 4:30am). It has been 3 weeks roughly and we have had some great nights where she slept from 7-6 (and then with me for another couple of hours) and only woke up once around 2 for a quick feed. Other nights (like last night) she still wakes up every hour or 2, but generally settles quickly without the breast. Around the time we made those changes, she started to be able to be settled in her cot (rather than me having to rock or feed or lie with her until she was asleep and then transferring her). I believe that has made thing easier.

Every baby is different, but I do get the impression that most babies have rotten sleep patterns around the 12 month mark.

My friend, who has done CIO or CC with her DS from the beginning had a very good sleeper on her hands, sleeping through from 6-5 since three months. But around his first birthday, she told me that he woke up lots of times. And because he wasn't breastfeeding and also wasn't used to being rocked, she had real troubles getting him back to sleep.

See if changing his day sleeps helps. Or if you give him more stimulation (playgrounds, etc.) during the day, he might be more tired at night. You could also see if it might be time to make minor changes or adjustments to his bed time routine. But, the main advice I can give you is: don't focus on his sleeping. Try and roll with the punches. If you get frustrated by his bad sleeping habits, he might pick up on it. And the last thing you want is him developing anxieties around bed time.

All the best, Sasa