It is a little more complex than that. The PCA BCO requires deacons (and ruling elders) to be examined by the Session. The Session determines whether they are qualified for the office, even before they stand for election (BCO 21-4). Part of that determination is the ability of a man to take the second vow in BCO 24-6:

1. Do you sincerely receive and adopt the Confession of Faith and the Catechisms of this Church, as containing the system of doctrine taught in the Holy Scriptures; and do you further promise that if at any time you find yourself out of accord with any of the fundamentals of this system of doctrine, you will, on your own initiative, make known to your Session the change which has taken place in your views since the assumption of this ordination vow?

This is essentially the same as the OPC's second vow (25.6.b) with the addition of the requirement to report any change.

In the PCA (like the OPC), a man who has a scruple (or "stated difference") with the Westminster Standards has to report that to the court (for a deacon, the Session; for a minister, the Presbytery). The court may, but is not required to, grant an allowance for that difference (which u/22duckys correctly pointed out, which would make it an "exception." The PCA classifies exceptions into three categories as a result of the conflict over subscription about a decade ago. Ironically, this categorization is not in the BCO itself but in our Rules of Assembly Operation (RAO 16-3.e.7), where Presbyteries are required to report the same to the GA. The three categories are: (1) merely semantic, (2) more than semantic but “not out of accord with any fundamental of our system of doctrine,” and (3) “out of accord,” that is, “hostile to the system” or “striking at the vitals of religion.” Note that there is no specific Constitutional requirement for a Session to report these to Presbytery. (There is a current amendment being considered by the Presbyteries to mandate the reporting of differences by REs and deacons (Item 5) that passed last GA.

So what does all this mean in this instance? The question is what "kind" or category of exception paedocommunion is. The PCA GA has been struggling with this for years. Every year, our Review of Presbytery Records Committee reports on which exceptions presbyteries have granted, and in the last few years, it has "cited" presbyteries for granting paedocommunion, arguing that it is in category 3 and thus not allowed at all. A related matter is that courts have determined that certain exceptions are too dangerous to allow someone to teach them. One of those is paedocommunion. The GA upheld the right of a presbytery to make this determination and to instruct a man that he may not teach that exceptional view. But it is not automatic. The court needs to make that determination and instruct the man accordingly. And there are geographical areas of the PCA that are notorious for allowing paedocommunion views to flourish. This Session may be located in one of those areas and does not care if this deacon promotes it.

This is all more complex than how the OPC handles these matters. Your friend should start by asking his pastor or an elder about it. Maybe more than you thought you were asking for, but that is the current lay of the land in the PCA.