I'm 37, can my legs still grow?
Your observations are confounded with time and lots of things can change in the intervening time, this include your flexibility (e.g., hips and/or hamstrings) and your components (e.g., your saddle). 

Flexibility, is often the first thing to change, if you were relatively inflexible in your hips you may have adopted posterior rotation of your hips (i.e., the top of your hips backwards) when riding, which could effectively shorten your leg length on the saddle.  This is often part and parcel with short hamstrings.  As flexibility improves you may have been able to rotate your pelvis to a more neutral position, which would have effectively lengthened your leg reach.  As an aside, flexibility  is also one of the first places people should look when they think they have a leg length discrepancy, structural leg length discrepancies are much rarer than asymmetrical flexibility.

Equipment can also change over time.  If you are running one of the classic leather hammock style saddles (e.g., Brooks) these can stretch and sag over time, which would lower the effective saddle height. Even some modern synthetic saddles can "break-in" (i.e., the supporting plastic frame becomes more compliant), which would cause the top of the saddle to sag a bit more than new when you put your full weight on it. This might be harder to pick up as the saddle should return to the original height when you get off, due to the memory property of plastics.

Sorry, you are not growing

It is highly improbable that you are growing at 37, as ~19-21 is the maximum age by which most people stop growing.  It is possible to develop a tumor that stimulates your pituitary to produce excess growth hormone, this actually happened to a friend, but since you have stopped growing in height this will result in your bones getting thicker and heavier not longer. Gigantism can also cause excessive height, but would have shown up earlier in life during your growth phase.