Hi George, it is so hard to say what normal is because we don't know if you're a teenager or a senior, if you're slim or have a heavy build, or if you're already fit from other sports you do. You are right, however, that when you get up to a 25K race you are likely to go out way too fast at first, unless you've done some proper pacing in your training. Hopefully you'll be working up to a training distance close to 25K before you actually run the race. If you've done proper training, you might be able to go a little bit faster on race day than in your training, just due to race day adrenelin. For me, I can run one mile in about 6 minutes, but that pace slows down to about 7 minutes per mile over a distance of 6 miles (10K), and slows down to about 8 minutes per mile over a marathon (42K). If I started a marathon at anything faster than my marathon pace, I'd be setting myself up for a poor performance.
One thing you can do if you're really interested to know what "normal" is: visit the website for the race you are interested in. The website should have a results section from previous years. You can then look up your own age category and see how fast and how slow people of your sex and age run that race.
But everyone is so different at running ability, even people of the same age, that it can be risky expecting to go at the average pace of your age group. You might be better off to just follow a good training program and your running pace will emerge over time. Don't worrry too much about what pace others will run - I can almost guarantee that some will be slower and some will be faster!
Good luck with your training.
