DS1 has one and enjoys it, but he got it at age 8. Really look at them and find one that goes to low weights. A lot of them are for bigger kids. We practiced quite a bit with me holding the pogo stick and him getting on and jumping. I'd keep my hands on it and help him with the balance.
DS1 has been on 2-wheels since his 4th birthday and does a Ripstik castor board and scooter really well.