I calculate that Sandy Hook is 972 years old as of 2007. If the maps show that the Hook grew 1-1/2 miles since the lighthouse was built in 1764 (243 years), and the Hook is about 6-miles from the entrance to the tip, then:
Divide Sandy Hook into four 1.5-mile sections (6 / 1.5 = 4)

Multiply those four sections by 243, each section taking 243 years (243 x 4 = 972)
results in an age of 972 years!

The lighthouse was built in 1764 at what was the tip (It's birthday is this June 11) , so it is 242 years old and a mile and one-half from the present tip of Sandy Hook.
How many feet does Sandy Hook grow in one year?

2007 - 1764 = 243 years
Growth was 1.5 miles in 242 years (7, 940 feet)

x / 243 = 7920 (feet) / 242 (years)
242x = 1720 x 243

242x / 242 = 1,924,560 / 242
x = 7, 952 feet in 243 years

7,952 - 7920 = 32 feet

Sandy Hook is growing about 32 feet per year!

We know the tip grew 1.5 miles since the lighthouse was built in 1764; and we estimated the mileage from the entrance to the lighthouse to be 4 miles. So the total length of the park is about 5.5 miles.

Therefore:
x / 5.5 miles = 243 years / 1.5 miles
5.5 x 243 = 13336.50
13336.50 / 1.5 = 891 years

Sandy Hook is approximately 891 years old!
And it must have started growing around the year 1116.
(2007 - 891 = 1116)