On our 35 night Ventura Caribbean cruise in January/February, we were among the youngest passengers, and it was a fairly quiet cruise. The previous August, again on Ventura, it was lively, noisy, busy and full of young families. Very different experience but both brilliant!
On our one and only FO cruise back in 2016, we really were the youngest couple, but the atmosphere was great. The older passengers were a great bunch and some of the more energetic ones were on the dance floor non-stop.