It's normal for me to have an erection when there's a big age difference with my sister, right? HUNTA-044

I'm a useless middle-aged man whose age equals the number of years I've been single. Although I have a cute younger sister who's 20 years younger than me, she always dresses very lightly at home, which makes me get an erection. Anyway, with such a big age difference, getting an erection isn't that weird, right? But then my sister caught me in the act, and she even walked over with a lewd grin...