Looking for Answers about Europe?

Mature is relative term. Just because you claim to be mature doesn't mean that NCL can make an exception to their rule. In most cases, the requirements are legal requirements of the country and not a corporate policy.
You can read more about the booking age requirements here
http://www.ncl.com/faq#age-requirements

The Blue Man show is free. The Cirque Dinner show is an extra fee and the fee varies as to whether you want premium seating or something where the view may be a little obstructed. Both are great shows and the Cirque show is well worth the extra charge.
We have sailed on the Epic on its 3 West to East Transatlantic voyages and love all of the venues for entertainment and dining..

There are no alarm clocks in the room but you can get a wake up call.

If you buy wine or Champagne and wish to consume it on board, you will have to pay a corkage fee. The fee ranges from $15-30 based on the size of the bottle.
However, if you want to just bring it back home, you can surrender the liquor and collect it on the last night of the cruise. That way you won't have to pay the corkage fees.

All NCL ships have Wi-Fi. However since the ship is mostly metal, the wi-fi signal may not be the best at all places. You can purchase minutes in blocks of 30/60/100/250. It costs $24 for 60 minutes and $100 for 250 min.

The shows on most ships don't need advance reservation. However, you can reserve the seats for the Blue Man Group on the Epic. You should be able to log into your account on NCL's website and make the reservation 45 days ahead of your sail date.

If you are a US citizen, you will not require visas.
It is always advisable to check the consulate website for rules regarding visas especially for tourists not from USA.
You can also contact NCL or your travel agent and they will have up-to-date information on the documents required for travel.

The summer has been warm everywhere. You should have plenty of opportunities to swim in Europe.

8 people may be too much in one room and you will have to split your party into two rooms.