Since going to integrated headsets, I don’t seem to need to service them.
Service tended to be “wait for it to go crunchy and chuck a new cartridge in” previously, and was maybe once every couple of years with a decent headset.
Edit – now I think about it, my last commuter had a cheapo £10 or so M part headset, and after literally tens of thousands of miles (more than 5 years worth) of all weather Glasgow commute I noticed a crack in the frame halfway through servicing it. I’m sure it was helped by the fact I was running a full mudguard so it didn’t get salty water splashed up at it so much.
I do remember having to service headsets a lot more often back in the day, so in junior’s case, maybe see if you could put a grease nipple on somewhere or replace with something better? Cane creek seemed good last time I got a non-integrated one, bearings lasted years and years – I may have replaced them once in 10 years or so.