I was just looking at that. Sri Lanka:
0-14 years: 24.7% (male 2,758,360/female 2,648,073)
15-24 years: 14.9% (male 1,651,901/female 1,606,465)
25-54 years: 42.1% (male 4,504,395/female 4,708,288)
55-64 years: 9.5% (male 966,295/female 1,117,310)
65 years and over: 8.7% (male 812,669/female 1,092,689) (2014 est.)
India:
0-14 years: 28.5% (male 187,016,401/female 165,048,695)
15-24 years: 18.1% (male 118,696,540/female 105,342,764)
25-54 years: 40.6% (male 258,202,535/female 243,293,143)
55-64 years: 7% (male 43,625,668/female 43,175,111)
65 years and over: 5.7% (male 34,133,175/female 37,810,599) (2014 est.)
Bangladesh:
0-14 years: 32.3% (male 27,268,560/female 26,468,883)
15-24 years: 18.8% (male 14,637,526/female 16,630,766)
25-54 years: 38% (male 29,853,531/female 33,266,733)
55-64 years: 5.9% (male 4,964,130/female 4,870,447)
65 years and over: 5% (male 4,082,544/female 4,237,592) (2014 est.)
Sri Lanka does have a much older population. And some of that larger over 55 crowd will be those western retirees I was mentioning. Some guy worth a couple million intent on spending his “golden years” in a “tropical paradise” has to skew the GDP a bit. It isn’t the entire reason, but I suspect it’s a contributing factor.
Sri Lanka is one country that offers an attractive retirement visa:
http://www.retiretosrilanka.net/visa