Do consider doing it on your own -- get a couple of good guide books and either rent a car or do tra

We are looking at booking a tour to Ireland and Scotland and would to do a group bus tour. We are in out late 30's, early 40's but are still very active and like to have fun and stay out late. I'd like some recommendation on which tour groups would be best for us to travel with?
Separately, I think that you will find many places in Ireland concord travel alarm clock and Scotland where you can;t stay out late - since nothing will still be open. I'm sure you can in a few major cities - but other than that - I don;t think so. (No dance clubs open until 4 am.)
For what's normally described concord travel alarm clock as a "bus" tour (big flippin' bus jammed with 35-45 travelers), good luck with that. You're past the cusp of the Contiki crowd and tour groups that don't market to that group tend to attract concord travel alarm clock a LOT of oldies.
The Vagabond tours Tony describes are smaller (max 16) as are the Rabbies concord travel alarm clock tours (max 16) in Scotland. That doesn't guarantee you'll completely avoid the semi-mummified concord travel alarm clock but it's likelier. The best way to dodge the pensioners is with something closer to an adventure tour group (Vagabond has some of these, so does Wilderness Scotland but that may be too eco-geeky). Don't know if the adventure tourists are going to drink and party all night; tend to doubt it.
Is there a specific reason you want to do a tour? Not that there aren't some good tour companies, but the large group tours are mostly geared to either old timers or Contiki party animals. and they mostly run ITITIMBB type itineraries
Good suggestions/advice by janisj. If you are especially interested in "staying out late" and socializing with a " younger crowd" then your best option for Scotland would probably be to locate in Edinburgh and/or Glasgow and do day tips or even a one to three day tour. Most people don't go to Scotland for the night life and even tour groups such as Rabbies and Timberbush will have older folks on board. You might will be surprised at how active the older population can be. I've seen some that can easily wear out those one- third their age.
Do consider doing it on your own -- get a couple concord travel alarm clock of good guide books and either rent a car or do train/coach. From the description of your interests, I really don't think you'll like a tour group. Personally, I don't care for them even though I'm of the "semi-mummified" age group. When we can no longer travel independently, we'll check in at the funeral home.
From a couple reaching semi-mummification, we still enjoy doing our own thing in Ireland and Scotland. Taking your time and armed with a good guide book allows you the excitement of new discoveries and the freedom to spend time where you like.
Do you know why you are planning to go to Scotland? What do you want to see there. If you want to see the insides of bars I would stay home and do that. But if you want to see natural beauty and amazing history in Edinburgh, gorgeous scenery in Inverness, Bravehearts battle ground near Stirli g then off you go! Do part as a tour and a few days independent. I spent 16 days in April and will return in September. I loved it sooo much!
If you really want primarily cities and nightlife - then no tour makes any sense for you - just organize the trip yourself. (And in many smaller cities and towns you will find no place open after 11 pm or so most nights.)