do you actually "train" for nighttime
According to my GP and a continence clinic that I've spoken to, no, you do not "train" for night time. I don't even call it night "TT".
As for when to get advice - my GP and the continence clinic say age 6 is when you can talk to somebody about it. Before that it's still well within the normal range for night dryness.
Both my 5yo and 4yo's are still wet at night. I use to worry about it with my oldest DS but I've been convinced now that there's nothing "wrong" with him, he's far from alone and I'll worry about it after he's 6.
Night wetting is also genetic, so if you or your partner were bedwetters as children, there is a high chance your children will also wet the bed. My DH wasn't dry until he was 6 according to MIL, so I'm hoping my kids will magically become dry at 6 as well!!
DS1 is using Dry Nites and DS2 still fits junior size nappies. I'll keep using them for now.