It depends on what kind of love you're referring to. Love of live, love for your family etc, you're right. That kind of love is not defined by age. Being "in love" is something different. That is defined by maturity.hell even kids can be in love
love isn't defined by age, nor is it restriced by anything else
A 40 year old and a 38 year old might think they're in love when it's really just lust and if they're not emotionally mature enough to realise that and they go ahead and get married, there's a good chance it'll end in a divorce at some point when they realise it's not love after all.
On the other hand, a boy and girl might meet in high school, fall in love and remain partners for life when they remain together after high school ends and they get married. That can happen too.
I should note that maturity is also not defined by age but it is also fair to say that age and life experience plays a big part in maturity.