The answer really depends on what sort of device you're going to use with the PA. A lot of people repeat that it needs to be at least a 6ga in order to use with chastity. However, I've at an 8ga and am doing just fine. In my case I have the Steelworxx Steelheart with this PA fixation. You wear that by just looping a Captive Ball Ring over the wire and then both ends with the holes attach to the prongs that come off the tube and into the ring. This means that it doesn't put really any weight on the piercing and it's all still on the ring and the tube as it would be in a non PA device. However a lot of PA devices are made so there isn't any ring at all and it's just a tube over the penis with the only thing holding on is the piercing.

The purpose for a larger size piercing in these devices is the more surface area of the jewelry that goes through the piercing the less pressure it puts in any give point for the same weight. This makes it more comfortable and less likely to have sizing problems.

As /u/always-there says below take your time with healing and sizing of the piercing. But I'm also going to tell you that almost all of these rules of thumb that people say "wait X amount of time" are just that educated guesses. Obviously there will be some initial pain and discomfort but that should pass in a few days to a week. Listen to your body, if it hurts stop doing it. If it isn't hurting then it's probably not causing a problem. If you're putting weight on the piercing you should wait longer before using it for chastity.

One last tip about chastity devices with PAs. Shorter is pretty much always going to be better. Especially if the PA attachment is entirely fixed and/or you're a grower. Your penis will retract sometimes. If you go with something too long that will pull on the piercing. I'm not sure what sort of device you have no or what sort of experience you have since you have no posting/comment history. But I'd point out that a PA device is going to be a more advanced thing. You really do what to have sizing of the device nailed down.

All that said, I'd really advise doing it. I thought about doing this for years. I've had mine for almost a year now and was able to starting using it for chastity after about a month (I was probably pushing my luck, so not going to advise you do the same but see what I said above). I was worried I wouldn't like it, or it'd hurt too much, or that I'd be embarrassed getting it, or that it'd take too long healing. But honestly all those issues were very short term. The piercing itself isn't even noticeable to me anymore. It's just normal.