You need 30 activity points to become Jr.Member.
You ACN attain max of 14 activity points in 2 weeks. So it take about a month to become a Jr.Member. after that you can participate in various ICO's. My advise, don't focus on levelling up, just help out people and see your level getting increased quickly. You also get merit points which help you in leveling up at later stages. Help is the key.