If your baby really doesn't like being on her tummy, leave it for now and try again another time. Bear in mind that babies develop differently, some more quickly than others. If your baby isn't rolling over by the time she is six months or seven months old, talk to your GP or health visitor.
Some men stop growing at 18, some at 21. Some men grow really quickly early on, and slowly grow taller until they have hit somewhere between 18 and 21, while others grow quickly later on and some just grow gradually. So, only time can tell you, no one else can because everyone is different.
1 Most girls start their sexual development between the ages of 8 and 13 (the average age is 12), and have a growth spurt between the ages of 10 and 14.  Most boys start developing sexually between the ages of 10 and 13, and continue to grow until they're around 16.