If you compete in local meets you may find that you are the only one in your age group or there are only two or three, so it is quite easy to get a medal which is always nice. If you check the previous years results you can see how many of each age group there were in each event.
People are generally very friendly and it is a fun thing to do. I entered two meets last year and got to dive off blocks for the first time ever (never having competed before). The older you are the fewer people in your age group there are likely to be.
Training with other people is also fun and will not ruin your stroke as long as you concentrate on your form when you swim. I have learnt how to swim faster by trying to keep up with people who are faster than me, I find it is quite hard to motivate myself to swim fast on my own. I know there are people on here who think swimming faster is not the point but it does actually give you a sense of achievement knowing that you can and beating your previous best.