As someone who has been singing at singarounds, clubs etc for at least 30 years, starting as a teenager, I have frequently been the youngest participant. Age has often seemd no more than a number, and I have been lucky enough to make many enduring friendships through music and song. Many of those apparently 'older' singers had taken up music 'later' in life so have been on a parallel journey in many ways. The vigour and passion in the delivery and banter of many of the singers at these clubs would certainly be described as 'young at heart'.
One of the great bonuses of gatherings of 'older' singers is hearing the wealth of material being shared - not just the songs popular today - but drawing on a wealth of material cherry picked over a lifetime. Then the sharing of tips and advice...
Perhaps its just where you feel comfortable, but I would never use age as an initial criteria