Allergic to cats?

So my sister and I grew up with cats and she's had one for about 6 years now. Recently, she told me that she's developed an allergy to him, he makes her sick, and she wants to give him to our dad. So I'm wondering how common it is to develop a cat allergy later in life. Has anyone heard of this as I am now freaking out that I will become allergic and have to give my cats away.

I grew up with 4 cats, and never had a problem until about 8 years ago. I take Claritan daily to still be able to live with my babies.

I was allergic to them all my life, till i hit my 20's. now i need a Claritan now and then, but otherwize i am fine. You can devolop a allergie at any time in your life, and your genes can pre-disposition you to certain ones. depends on what runs in your family too.

I have had cats my whole life and allergies to them for the same time ... I wash my hands alot .. take hoemopathic allergy pills ( they work far beter than any RX that I have been on) and grin and bear a little .. oh I dont have fluffy longhairs since they bother me more than shorthairs..