With regard to legality of sale of nicotine replacement, it is my understanding the the UK gov. is planning to allow sales of NRT in places where tobacco is now sold. This of course is a long overdue measure, last time I tried to give up , ran out of gum at 6.00pm, ended up buying a pack of cigarettes from the local garage, oh well.
How this relates to an airlines legal position I have no idea, as for instance duty free sales are allowed for 17 yr olds traveling from UK to say US, where the legal age in both countries is over that.
I believe it would depend under what conditions you wanted to dispense NRT.
1. If to passengers craving a fag, and you were handing them out for free, probably under the same considerations as giving them a painkiller for a headache.
2. If for sale, as a service to passengers, like alcohol on a charter flight, some sort of regularity approval may be required. No idea what though.