Its a trap! There is no general ABV to age spirits at. Its just another one of those spectrums that we have control over to push flavours in a certain direction. Generally, the goldilocks zone is between 50% and 60% ABV (100 and 120 proof). Aiming for the 50% side of things will give more sweet, caramel and vanilla flavours. 60% more spice, pepper and tannin. Have a think about the kinds of spirits you enjoy drinking. What flavour profiles do they have? Use those preferences to pick a ABV that may be best for you. Give it a shot, assess it and then change your approach next time based on these results.