Yes it's okay to get a tetanus shot before 10 years if you want too.
I get a tetanus shot every 5 years myself just to be safe and sometimes if I wait up to 10 years between tetanus shots I sometimes forget to get a tetanus shot and then I happen to step on a nail or get another injury that could potentially lead to a tetanus infection.
If you haven't had a tetanus shot within 10 years then you should get a tetanus shot within 48 hours of getting injured with something that could cause tetanus.
After having 3 tetanus shots my doctor said that I should be immune to tetanus so after 3 tetanus shots you shouldn't need anymore tetanus shots even if you get injured.
But it's not gonna hurt anything other than your arm to get another tetanus shot if it's been 10 years or more since your last tetanus shot.