Is it normal for my guy to like my little pony?

Depends on how much of a fan he is? Because whenever someone mentions a My Little Pony fan who isn't a 12 year old girl, I think of this guy.

It isn't bad to like a kids show, but if he refers to himself as a "brony", then you should probably be worried

There is a whole group of them called bronies.

Little pony is amazing!

Yeah,probably is !

Hard to give you a real answer as I've never bothered to ever watch it.

It's a rather subjective issue if you can even refer to it as an issue as there's nothing wrong with watching a show that some might perceive as having a target demographic that supposdly aims for a much younger fan base. Yes it might challenge some people's perception of what older males watch but again it's all subjective. I have watched it myself and In my opinion its a rather mature show ( even more mature then some pieces of media intended for a older demographic) that teaches morals and often uses humour to enthrall the viewer. It's vastly improving as the seasons go on with character development and changes to the overall plot being implemented. 

The show is very aware of the adult fan base it has attained and as such many episodes now deal with subjects one might be surprised to see in a children's show one instance I can think off is the season 5 premiere whitch deals with communism and compares individualism to conformity.