Some go into the booster seat before they r 2 yrs old. Now the law is enforcing that kids be in booster seat til they turn 8 yrs old. Mine has long legs so I had to switch them around 15 or 16 months old.They weighed over 30 lbs too. Going by what your child can do is alot safer than going by age. If your child can sit without support, and hold his own head up, and is at least 24 pounds ( a little less is okay.) Then is is probably okay to put him in a booster seat.