I got Peanut Butter when he was 1 month old. At that time my Hazelnut was 7 months old and a very laid back, cuddly pig. He never bothered PB, but the moment PB became a "teenager" he was mounting Hazelnut. He still does it and PB is 2 years old and Hazelnut will be 3 in November. No other problems though, just the mounting. Hazelnut just shrugs him off and PB popcorns. This happens about 2 or 3 times a day. We only had one bad episode where in his early hormonal phase, PB spent an entire day chasing and mounting Hazelnut. When he got boar glue all over Hazelnut, H had had enough and proceeded to chase a squealing PB all over the cage until I took H out to clean him up. Since then it is just the normal ritual of PB mounts H, H shrugs him off, PB popcorns.
So, if mounting is the only thing I wouldn't worry but just keep an eye on things as others have suggested.