Does Japan have an ageing population?
I hate to sound rude, but you could easily answer this yourself with even the most minimal look into well-tabulated demographic information, rather than highly non-representative observations. About 13% of Japan's population is 0-14 years old, the third lowest fraction in the world. (https://data.worldbank.org/indicator/SP.POP.0014.TO.ZS ; easy to find with Google)  The fraction of the population over age 65 is 28%, the highest in the world. (https://data.worldbank.org/indicator/SP.POP.65UP.TO.ZS?most_recent_value_desc=true) The population density is high, so you'll certainly see more kids than in many other countries, though not proportionally more. I will leave it as an exercise to look up the numbers for Tokyo itself.