Welcome to the forum! I took a break on and off for about 4 years and there are some things you never forget. Like posting. I feel like once you learn to post, you will always remember it! But your leg may have forgotten how to stay in the correct place and even if your legs are strong for other things, most things don't require you to use your horseback riding muscles. I also find that people who take a break for that long are a little unsure the first couple of lessons so it's nice to have a solid school horse that will take care of you and someone on the ground watching. Like a few have mentioned, I would highly recommend taking some lessons first, just to help you get back into the swing of things. That's great that you have the opportunity to possibly lease a horse!