Quite simply, everything feels a bit... watered down to me. I still feel emotions, just not quite as strongly. For example, my grandmother is visiting for the first time in about a year, yet I don't feel much of anything. No excitement, no happiness... Is it just me growing up, or is there something "wrong" with me(for a lack of better terms)?

dont worry about it, alot of people are like that now a days, but most just put on a fake enthusiasm for moments like that

I don't really like pretending to be enthusiastic. I'm bad at it and it feels insulting when people act like towards me. But I suppose it's not necessarily a bad thing.

That is no problem. We will often be surprised by our own responses to situations. A close friend of mine died of cancer last thursday and I did not cry. I still am yet to feel the overwhelming wave of grief that is stereotypically associated with such situations. This is not to say that I'm unusually strong. This is just me.

Don't let anyone dictate what you 'should' feel. Different people work differently - but at the same time, there are a lot more people like you than you think! There could be many reasons that explain why you're not absolutely over the moon about your grandmother visiting. Maybe you just aren't incredibly fond of her. Maybe your emotions for her diminished over her absence. Maybe she's just not a lot of fun. Maybe you'll feel differently after she's been here for a while.

Feel what you feel, and if it bothers you, see a doctor.

They'll probably tell you that you're normal.
Don't worry bro.

Your'e just feeling a lack of excitement in life.. like Saika said.. DON'T LET ANYONE DICTATE WHAT YOU "SHOULD" FEEL.. Just be you..