So how much money does it cost to go in, and rent a pair of skates, and what is the age they consider someone to be a kid

I didn't rent skates but believe the admission and rental for the day is approximately $16...in the ballpark

Admission Adults: $7.00 weekdays; $10.00 weekends (starting Friday 7 p.m.); $10 holidays Seniors (60 & older): $7.00 weekdays; $10.00 weekends (starting Friday 7 p.m.); $10 holidays Children (12 & under): $7.00 weekdays; $10.00 weekends (starting Friday 7 p.m.); $10 holidays Skate Rental: $6.00/person. You must wear socks to rent skates. Lock Rental Coin-operated lockers are available for rent ($0.75 per use). See website for more info: https://www.nycgovparks.org/facilities/iceskating/10

The pricing should be on their website