Most TT's are either club run or under the USAC umbrella. Both usually go by category and age category. Usually though, they're not done by age group only. That's pretty common and the only way I've seen triathlons and running stuff go, age group only and "open" classes. Bike racing is a touch different, the age groups for older athletes are also in a category (masters 4/5, masters 3/4, etc...).
Either way, times are super dependent on a wild variety of factors.
Either way the roughest I can say is if it's 50ft per mile or so..........times will be 20-35min for a 10mi and do the math from there for a 25mi TT and so on. Either way, it's going to a threshold effort. So, plan your training accordingly.
If you've got a similar route nearby, do a practice run and get an idea of your time! Zwift or online calculators don't do it justice.
Get ready for the local Ironman triathletes to show up and register as a Cat 5 or Cat 5 masters on a day-only license and wind up with fastest time of the day.