Timeless, as what we define it, is something that's lasting, enduring, permanent, undying, immortal and everlasting. So timeless love isn't restricted to a particular date or time. The feelings doesn't change as the years go past.
Need help expressing your feelings? Below are some of the best love quotes online that nail what it really means to be in love (from YourTango.com):
"The best love is the kind that awakens the soul; that makes us reach for more, that plants the fire in our hearts and brings peace to our minds. That’s what I hope to give you forever." — The Notebook
"The greatest happiness of life is the conviction that we are loved; loved for ourselves, or rather, loved in spite of ourselves." — Victor Hugo
"And remember, as it was written, to love another person is to see the face of God." — Les Miserables
"The best and most beautiful things in this world cannot be seen or even heard, but must be felt with the heart." — Helen Keller
"I saw that you were perfect, and so I loved you. Then I saw that you were not perfect and I loved you even more." — Angelita Lim
"I swear I couldn't love you more than I do right now, and yet I know I will tomorrow." — Leo Christopher
"If you live to be a hundred, I want to live to be a hundred minus one day so I never have to live without you." — A. A. Milne
"You don't love someone because they're perfect, you love them in spite of the fact that they're not." ― Jodi Picoult, My Sister's Keeper
"I would rather spend one lifetime with you, than face all the ages of this world alone." — Lord of The Rings
"Being deeply loved by someone gives you strength, while loving someone deeply gives you courage." — Lao-Tzu