First of all congratulations on getting started in gymnastics. It is a great sport and will benefit you in many different ways.
It is not advisable to get into grips too early. At first your hands need to learn to grip the bars correctly on their own. The dowel on the grips will do this for you and if you don;t spend a decent amount of time working bars without grips you will not learn this properly. Having said that though because you are older you may need grips earlier on in your training than a younger girl. Because the heavier you are the more pressure there is on your hands.
In our gym the girls usually get grips around level 4, this is because at this level the girls are training a lot more (4-5 days a week) and will need to spend more time on bars and their hands need to last longer. I would reccomend if possible leaving grips until you have a really strong kip with straight arms. By the time you have mastered the kip with straight arms you should have enough understanding of grip to move safely to using grips. You will find they are useful for the skills like clear hips and giants you will learn after kips. If you have not got your kip yet, or if you have it but are still inconsistent or bending your arms I would only reccomend grips if you are one of those people who rips easily. You could even have this as a reward for you. - get gaurds when I master the kip.
If you are doing this go straight to the dowel grips, but if you ca't resist and get grips early go for the non dowel grips.
As for joining the team, that will vary a great deal from gym to gym. Some gyms will only out their most talented gymnasts on the team. Other gyms will have every gymnast who reaches level 3 or 4 on the team. Some gyms only start their teams at level 5, most at level 3 or 4 and some as early as level 1 or 2 so you will need to find out what the policy is at your gym.
Some gymns will not allow a girl of your age to join the team. Preferring instead to put new 6-8 year olds on. If this is the case, look for another gym. It is a crazy policy and I belive a person should be able to join the team at 50 if they have the skills, the dedication and the committment.