It depends on your experience. Have you been mostly studying for higher degrees, holding a non-business related role, or have you already had quite a few years industry experience that is business related? If it is one of the first two scenarios, then 28 for BA is not an issue at all. If it is the 3rd scenario, then you might want to assess whether BA is the right level, or you should try for the next level e.g. associate/consultant.
Regardless, one thing that you need to be comfortable with when joining at 28 is that you need to let down the ego and don't compare yourself to others purely by age. Know that you will have colleauges who are younger than you but higher in rank, but also appreciate that they do have accumulated much more experiences and expertise in this specific field, so they deserve the higher rank. The progression and rank in consulting is earned by hardwork, not seniority in age nor short-cut. So if you want to be in this field, you have to play by the rule willingly.
Hope it helps,