I agree with the fun class too.
My DDs do gymnastics and both are competition girls.
My eldest is 8 and she now does 12 hours a week. She does competitions for the county, regional and (next year her) national grades.
My youngest has recently turned 5. She is in a class of other 4 and 5 year olds (all reception year) selected for competing in the long term. At the moment she does one hour a week, and soon that will increase to two one hour sessions. I think that is enough for now.
My eldest DD has been doing gymnastics since she was 3 (and joined the development squad the term after she turned 5, doing 3 hours a week), and whilst she is good, there are some girls who didn't start until they were 6 or 7 and they have more than caught up. One girl in particular is very good, and I would say a fair bit better than my DD (although she is also almost a year older than my DD), so starting them early does not necessarily mean that they'll be better. Over the past 5 years of watching my DD do gymnastics I have seen girls come and go from the squad... and my observation is that they have to enjoy it to stick at it. There are (will be) times when it is difficult, when they can't get a new skill etc and if at heart, they don't enjoy it, then they'll just give up.
Good luck with it. I find gymnastics a real roller coaster of emotions. I didn't know what I was signing up for when my DD1 started (only sent her along so I wouldn't kill her she could get rid of some of that excess energy) and I'm always going between feeling very proud of my DD, not wanting to be a pushy mum, worrying that what she is doing is safe and not causing her long term damage, resenting the hours she spends training and wondering what the bloody point is seeing as it is highly unlikely she'll ever be a professional gymnast and wanting to support my daughter.