Without knowing the exact details of the 'night call visual novel', it's hard to say for sure. If it's more of a family - friendly exploration of night - time activities, like a story about a kid's adventure during a sleepover at night, then yes, it could be suitable for all ages. But if it delves into more serious or potentially disturbing topics like crime at night, it might be restricted to older audiences.
There's no way to be certain without further investigation into the 'night call visual novel'. If it is mainly focused on positive aspects of the night such as the beauty of the night sky and simple nocturnal animal behavior in a fictional and educational way, it could be great for all ages. But if there are elements like psychological thrillers with dark undertones that might be too much for younger minds, then it would not be appropriate for all ages.