I have to stress I got my nose pierced at 18, my tongue at 21 and my labret 3 months ago, and I'm 30. So not a teenage "rebellion" thing there! lol
My tongue healed very quickly. I had trouble eating solid food for a couple of days, but it was fine after that. No slurring, no difference in my speech at all. But then everybody is different!
Just keep an eye on it, and if it starts hurting, or oozing stuff, give your piercer a call. Tongue piercings should be clean, albeit a bit swollen in the first couple of days. Keep doing the mouth washes after you eat anything, drink anything, or smoke. Non-alcoholic washes are best. Oral B does one.