My 12 yr old son is very keen on roller blading. He can do all kinds of tricks now - skating backwards, jumps etc - and it is very good exercise. He also gets a lot of knocks and bruises, though.
The main problem for us is that he wants to use the ramps provided in various parks but there are often teenage yobs hanging around. If you just want to skate along paths, though, that won't be a problem and it is still good exercise.
We got his last pair of boots from JJB - a pretty decent pair for �50.
It might be a good idea to wear some padding around your rear end when you start! Good luck!