So enjoyable that you don't want to stop (adj)
Addictive
/əˈdɪk.tɪv/
Making you feel extremely tired (adj)
Exhausting
/ɪɡˈzɑː.stɪŋ/
A young person below a particular age who is involved in an activity, especially sport
Junior
/ˈdʒuː.njɚ/