I don't think it is a bad idea to raise the minimum age as long as they still cater for younger gymnasts to have plenty of opportunities to compete at the appropriate standard.
One of the idea's of raising the age is to reward those who stick with the sport longer. It is quite sad to see many of those olympic champions devote their whole childhoods to gymnastics make the olympics at age 15 and then drop out of the sport altogether as they have achieved their ultimate goal. One of the problems we face in gymnastics is keeping older gymnasts in the sport. many gymnasts have a wealth of 5-10 year olds but only 1 or 2 teenagers and adults.
The age of athletes at an international level seems to be increasing anyway. In the 2000 olympics the two oldest gymnasts were 21, by 2004 there were gymnasts competing in their mid twenties and even early 30's which is not uncommon at all now on the international circut. This is because I believe first of all the skills in womens gymnastics are changing, there is less emphasis on lightness and flexibility and women seem to be adopting many of the skills men do. These skills require incredible strength and 15 and 16 year olds are far from their peak of strength. Females should continue to get stronger through out their 20's and hit peak strength around the age of 30, and should be able to maintain peak strength for quite a while after that. Very few do because they drop out of sport and look to other interests and pursuits. Also there is more money in gymnastics now, in the past teens had to quit gymnastics by about age 20 to get a job and support themselves, training full time was simply not an option. This is all changing. Our sport needs to change with the times.
However, this will all only work if the younger teens have high level competitive opportunities and the chance to compete against the best juniors in the world. This needs to be paid strong attention too because these juniors will be the future of our sport.