So second pp Tiger cubs is 1st grade. You can start any time during the year, just contact the local pack and tell them you want to sign up. If you are not sure who to contact just check with your local churches, the pack will be chartered thru one of them. If you don't want to go that route you can also go online and find them thru the national council website.
But to correct pp Tigers is no longer the first year you can start - at least not everywhere. There is actually a pilot program that they just started in some parts of the country for kindergarteners. They are called "Lions". It's the rebirth of a program from the 50s believe it or not (My father was one). You'd have to ask at council level if the program is available in your area.