Hi there,
The legal age for smoking across Ireland is 18.
No one can smoke in bars or other restricted areas.
Regarding the Shicha, there are some Shisha bars in Dublin, but again if you are under 18, you may not be able to go there without someone over 18.
How many days are you staying in Dublin? There so much to see and do maybe there will be some activity that will interest you.
Personally, I love the watersports; you can Kayak along the river or even try
Windsurfing!
What type of activity do you like?