Relationships are the same way, except for maybe the simple part. It can be really difficult to find a relationship when you'd like one, and when you have one it can be hard to accept your partner's shortcomings and make things work.
Your partner is in his fifties. Something you should take into consideration is that peoples' sex drives can diminish as they age. The men you dated when you were younger were probably younger than your partner, and that is why the sex was frequent. You're getting older, too - maybe your sex drive hasn't changed but you aren't as youthful as you once were.
You were your partner's first. There was an adrenaline rush as he was introduced to sexuality and a honeymoon phase of a new relationship to bolster the happiness. But now maybe his years are catching up to him.
This is the part where you either communicate and try to make compromises, accept that your partner doesn't check all of the boxes, or decide you need something more and begin the search for love all over again.
Just keep in mind that it's hard to find relationships. It can take years, and a lot of heartbreak. And, a lot of work. It's okay if you decide this person isn't for you, and it's best to decide that sooner rather than later so you aren't wasting each others' time. But decide if it's worth keeping and working at first.