Wow! Congratulations on your marriage. Obviously, something has been working within that time. But, I hear ya. Many people struggle with this in long-term relationships.
First, I like to say that nothing will ever make it exactly as it was. We cannot go back in time to when the relationship was new and exciting – it’s been too long. That doesn’t mean you are condemned to a boring or passionless marriage, though. What it does mean is that you have to find new ideas and make a real effort. I’d gather that notion is not very different from what has made the rest of your marriage work for so long – there’s work involved.
I challenge my clients to come up with a “bucket list” of sexual/intimate ideas … you know, things that may sound interesting and that you've never tried but always wanted to. It might even include things you may have tried once ages ago and liked but never attempted again. Both of you can throw out some ideas, as many as you want. Do you want to try kink? Do you have some sex toys collecting dust? Have you ever watched porn together, or read erotic fiction? What about trying new sex positions and new locations in the house outside of your bedroom? Once you have some ideas down, start taking these ideas for a spin. Find ways to incorporate them into your current sexual repertoire. Have some fun. Be willimg to experiment; if you don’t enjoy it, you don’t have to do it again.
It may also help to discuss context – what really gets each of you in the mood to be intimate/sexual. Take time to recreate said context for each other; again, not all at once. If one of you is more a hearts and flowers context person, go out for a nice date once in a while and allow enough time afterwards to be intimate before the night is over. If time is a factor, figure out what time of the day best suits you both to avoid feeling rushed (unless a quickie is the point).
Also, it helps to note that as we get older, life happens. We get older, and our bodies and our minds age too. This brings a whole host of other considerations that can impact our sex lives. I recommend striving for quality over quantity. Have a sex life worth having, however you define that.